Liz Mair, a former aide to Scott Walker, who was fired after sending out critical tweets about the Iowa caucuses last spring, was back on Twitter on Monday to offer some analysis about the Wisconsin governor's exit from the presidential race.

Mair, who has worked on several national political campaigns over the years, called Walker's campaign doomed from the onset.

Here are some tweets.

Hillary Rodham Clinton returned to Little Rock, Ark., on Monday for a grass-roots organizing event in her old stomping grounds.

Clinton served as first lady of the state during former President Bill Clinton's tenure as governor.

Earlier in the day, Clinton traveled to Baton Rouge, La., where she lauded President Obama's federal healthcare plan, and vowed to continue to "bring down healthcare costs for families" and "ease burdens on small businesses."

Before her arrival, Louisiana Gov. Bobby Jindal, who is seeking the Republican presidential nomination, assailed her visit. He has blocked Medicaid expansion under the Affordable Care Act in his state.

"After all, Secretary Clinton is the godmother of socialized medicine," Jindal said in a statement. "Obamacare was sold to the American people based on lies that it would improve quality and lower costs. It has done none of that and needs to be repealed."

Wisconsin Gov. Scott Walker, who as recently as midsummer was seen as one of the leading candidates for the Republican nomination, quit the race Monday, according to a campaign official, the second high-profile dropout this month in a campaign reshaped by voter demand for candidates outside the ranks of traditional politicians.

Walker's departure from the race follows that of former Texas Gov. Rick Perry. Both men quit after rapidly fading polls led to dwindling campaign donations. In Walker's case, the decline was particularly steep -- he was in second place in some polls early this summer, but lost nearly all his support. A CNN/ORC poll released Sunday had him at zero.

Donald Trump, who is not shy when it comes to ranting on Twitter, used the social media platform Monday to take questions from followers.

Would he forgo the presidential salary of $400,000 a year?

"I won't take even one dollar," said the billionaire businessman.

What's your stance on gun control?

"I am very pro 2nd Amendment. So important and I believe in it 100%. ... Very pro 2nd Amendment," he said.

Many of Trump's responses were vague and offered few details -- which critics of his insurgent candidacy have called a weakness. Still, despite offering little details in terms of national security or job creation -- other than rhetoric for the most part -- Trump has consistently remained atop the polls this summer in his quest for the GOP presidential nomination.

Trump held the session in Twitter's New York offices and was the first candidate to use its new Q&A; tool, according to the company. Throughout the 2016 election cycle the company will look to work with politicians on both sides of the aisle.

A half-century ago, the question on the campaign trail was whether America would elect a Catholic president.

This week, as millions in the U.S. prepare to embrace the visiting Pope Francis, the question of a religious test for political participation arose anew -- this time regarding Islam.

Republican candidate Ben Carson told NBC's Chuck Todd over the weekend that he didn't believe a Muslim should serve as president. An advisor said Monday that Carson will not apologize for "telling the truth."

The issue bubbled up after Donald Trump, the front-runner for the Republican nomination for president, declined during a rally last week to correct a supporter who insisted that President Obama is Muslim and asked about Muslims, and "when can we get rid of them?"

"We have a problem in this country, and it's called Muslims," the man told Trump. "You know our current president is one." Trump was perhaps the most prominent member of the birther movement that questioned Obama's birthplace; the president was born in Hawaii. His mother was American and his father was Kenyan.

Yet the man's other comment, wondering when we can "get rid of them," was more troubling, as was the fact that it has been overshadowed by the assertion on Obama, said Akbar Ahmed, chair of Islamic studies at American University in Washington, who is working on a book and a documentary about the subject

"A man publicly recommends ethnic cleansing in America to the leading Republican candidate," but the media focuses on his misrepresentation of Obama as a Muslim, Ahmed said.

"Yet the commentators are mostly silent on that," he said. "There's an endemic Islamophobia."

The ugly back-and-forth lingers just as the country embraces this week's visit of the holy father of the Catholic Church, with many non-Catholics as excited as Catholic Americans about Francis' tour of Washington, New York and Philadelphia, his first trip to the U.S.

Even half of those who take a dim view of the church see Francis positively, according to one recent poll.

That's a dramatic change in viewpoint from the 19th- and 20th-century resentment of Catholics immigrants, and a simmering prejudice that caused Americans to ask whether the Catholic John F. Kennedy would, as president, take his orders from the pope.

Muslim Americans await such a cultural evolution.

"At what point will Muslims break in like Catholics, Italian immigrants, Jewish immigrants?" asked Ahmed.

On the question Carson answered, whether a Muslim can be president, the founders spoke clearly. The 1st Amendment protects freedom of religion, and Article VI of the Constitution rules out any religious test for public office.

"It's unimaginable that the leading GOP presidential candidates are resorting to fear-mongering to benefit their campaigns," Rep. Keith Ellison, one of two Muslims in Congress, said in a statement. "And every American should be disturbed that these national figures are engaging in and tolerating blatant acts of religious bigotry."

Ballot access deadlines and other logistical hurdles won't take precedence over family considerations as Joe Biden ponders a run for the White House, the vice president said in a new interview released Monday.

“For us, it's a family decision, and I just have to be comfortable that this is, that this'll be good for the family,� Biden told America magazine in an interview conducted last Thursday about Pope Francis' upcoming U.S. visit. “It's not quite there yet. And it may not get there in time to make it feasible to be able to run and succeed, because there are certain windows that will close.�

“But if that's it, that's it. But it's not like I can rush it,� Biden continued. “It either happens or it doesn't happen. I know that's not satisfying to anybody. But people who've been there, I know they understand.�

Biden's eldest son, Beau, died May 30 after a battle with brain cancer, upending the timetable for the vice president to make a decision about what would be his third bid for the presidency. As an independent “Draft Biden� political movement has worked to build support and the vice president's closest advisors have sought to keep all options available to him when he is ready to decide, polls have continued to indicate interest in his candidacy.

But even as he's engaged in public events that offer a glimpse of what his campaign could look like, Biden has consistently maintained that he would not run unless he could give it the full commitment it requires.

Interviews like this one, and another conducted recently with late-night TV host Stephen Colbert, suggest Biden may be far from making a decision.

But there were also some clues that could indicate the opposite.

Biden noted that the past campaigns he's run “have actually strengthened the family,� and that politics has become something of a “family business.�

He also revealed a message he received from the widow of Edward M. Kennedy, discussing how the late senator's family would deal with similar grief -- by dedicating themselves to the causes of those who'd passed on.

“That's the decision we've all made, that regardless of what I do in public or private life, we are not going to walk away from the things that made Beau's life in his mind, beyond his family, worthwhile,� Biden said.

The vice president will have a prominent role this week as Pope Francis visits the United States for the first time since becoming the leader of the Roman Catholic Church. Biden will join President Obama on Tuesday in welcoming Francis to the Washington area and will participate in meetings at the White House on Wednesday morning and attend mass in the afternoon.

Thursday, the vice president will attend the pope's address to a joint session of Congress. On Sunday, Biden will travel to Philadelphia for a departure ceremony as Francis ends his trip and returns to Rome.

-- Michael A. Memoli

Donald Trump's second-favorite author, Donald Trump, is set to release a new book next month. And it's probably going to be huuuge.

Threshold Editions, an imprint of Simon & Schuster, will publish the Republican presidential front-runner's latest book on Oct. 27. The book is as yet unnamed, but if his previous efforts ("Trump: The Art of the Deal," "Trump: The Art of the Comeback," "Trump: The Best Golf Advice I Ever Received") are any indication, the title will probably include the name "Trump."

"The Art of the Deal," published in 1987, is Trump's first book, and probably his best known. At a campaign event in Michigan last month, the real estate mogul declared that it his second-favorite book of all time, after the Bible.

Simon & Schuster says the new book "will outline how a crippled America could be restored to greatness."

According to a news release, "Of particular interest will be his vision for complete immigration reform, beginning with securing the borders and putting American workers first."

Ben Carson has no need to apologize for saying the U.S. should not elect a Muslim president, a spokesperson for the candidate said Monday morning.

Speaking to CNN's "New Day," Armstrong Williams said, “You don't need to clarify what you believe in -- It is who you are . . . He believes in telling the truth. You may not like the truth, but it is the truth."

"When you tell the truth," he said, "there is nothing to apologize for.“

Over the weekend, Donald Trump defended his decision not to challenge a supporter who asserted during a Trump town hall that President Obama is a Muslim.

Speaking on the subject at a conference of conservative Christians, he added that he would fight to protect their right to practice Christianity inside the U.S.

This morning, he adds more thoughts on the subject, quoting tweets of Christian Broadcasting Network anchor David Brody:

Following last week's marathon debate at the Reagan Library, Republican presidential hopefuls headed back out on the trail and made the rounds on the Sunday talk shows.

Here's all you need to know to start your week.

>Donald Trump refused to apologize for not defending President Obama when one of his supporters called the president a Muslim.

> Ben Carson even weighed in on Muslims in America, saying that he would not want to see a Muslim president of the United States. It's not the first time Carson's rhetoric has raised some eyebrows.

> Hillary Rodham Clinton wants the United States to accept nearly 65,000 Syrian refugees next year. Speaking on CBS' "Face the Nation," Clinton said the situation in Syria is the "worst refugee crisis since the end of World War II."

>New polls showed a bump for Carly Fiorina after last week's debate, but she still trails Trump, who has been the front-runner for much of the summer.