Donald Trump continued his spat with Jeb Bush over the Sept. 11, 2001, attacks, implying that had he been president at the time, things "would have been much different."

"I am extremely, extremely tough on illegal immigration," the Republican front-runner said on "Fox News Sunday." "I'm extremely tough on people coming into this country. I believe that if I were running things ... I doubt that those people would have been in the country."

All of the Sept. 11 hijackers entered the country on U.S.-issued visas. However, a federal report did find that they all broke immigration laws -- for example, some used fraudulently manipulated passports.

Bush fired back at Trump on CNN, reiterating that his brother, then-President George W. Bush, "responded to a crisis ... and he kept us safe."

He also said Trump is not taking important issues seriously. "Across the spectrum of foreign policy, Mr. Trump talks about things as though he's still on 'The Apprentice,'" Bush said. "As though it's some sort of board game."

But Trump is not the only one challenging Bush's assertions about his brother.

That briefing, made public in 2004, contained no specific warning of the looming attacks on New York and the Pentagon, but it provided fresh information that Al Qaeda was bent on hitting targets in the United States.

When Rand Paul entered the GOP presidential race, he sought to stitch together a distinct coalition: his father's fiercely loyal libertarian supporters, millennials and others new to Republican politics whom he hoped to draw with his provocative stances on privacy and marijuana laws.

Six months later, none of that is working.

As the Kentucky senator struggles, a sometime ally turned rival, Sen. Ted Cruz of Texas, is working hard to court voters who adored Paul's father. Paul's strategists had assumed that voters enamored of former Rep. Ron Paul, a Texas libertarian, would be the bedrock of his support.

Cruz, a fellow product of the tea party movement, is beginning to pick up support just as Paul is losing it.

"Saturday Night Live" began with a 10-minute spoof of last week's Democratic debate , putting guest star Larry David in the spotlight as Sen. Bernie Sanders.

David infused the character with hoarse, forceful irascibility, holding forth passionately about big banks and super PACs, along with a couple of "Seinfeld"-style "What's the deal with ..." rambles.

Sanders apparently enjoyed the way his fellow Brooklyn native portrayed him. "I think we'll use Larry on our next rally. He does better than I do," he said on ABC's "This Week."

"SNL's" Kate McKinnon played a more pragmatic-minded Hillary Rodham Clinton, with frustration and ambition often breaking through the character's carefully crafted facade.

Taran Killam as Martin O'Malley, Kyle Mooney as Lincoln Chafee and guest star Alec Baldwin as Jim Webb rounded out the pack.

Watch the sketch above, and click "read more" below for analysis of the real-life debate.

Is Rep. Paul Ryan a "true conservative"? Sen. Ted Cruz won't say.

Ryan, the Wisconsin Republican who was the GOP's vice presidential nominee in 2012 and now chairs the Ways & Means Committee, has been viewed for years as one of the intellectual leaders of conservatism. But ever since Republican leaders started talking him up as a candidate to become speaker of the House, some on the right have argued that Ryan isn't conservative enough.

Asked repeatedly in an interview on NBC's "Meet the Press," Cruz, the tea party favorite from Texas, refused to vouch for Ryan's conservative bona fides.

"I like Paul Ryan. He's a friend of mine. This is obviously a question that is wrapped up in the speaker of the House deliberations," Cruz said. "I have said consistently I'm going to stay out of that."

With the government now just a couple of weeks away from hitting its credit limit, Republican presidential hopeful Ben Carson said Sunday that Congress should raise the ceiling on government debt.

What to do about the debt ceiling has deeply divided Republicans, with many GOP members of Congress opposing any increase.

But Carson, the retired neurosurgeon who is among the most popular GOP presidential hopefuls, said there's not much choice.

"I recognize that our backs are up against the wall in a couple of weeks, and we have to do that in order to prevent a default. I do know that," he told ABC's George Stephanopoulos.

"However, this should be the last time we have to do it," he said.

Without an increase in the debt limit, the government would be unable to pay all of its bills. The Treasury Department estimates that the government will hit the limit around Nov. 3.

House Republican leaders have a tentative plan to vote this week on a bill that would partially raise the limit. It would allow the government to pay interest on its bonds, which would avoid the possibility of a potentially catastrophic default.

Democrats oppose that idea, saying it would put the government in the position of sending checks to foreign holders of U.S. bonds ahead of making payments for veterans benefits, salaries for government workers and other domestic expenses. They say Congress should simply increase the limit, as it has done repeatedly in the roughly 100 years since the cap was first put into place.