Republican presidential candidate Ted Cruz muscled into the immigration debate Friday with his own plan to end President Obama’s executive actions, do away with birthright citizenship and increase deportations.

“We have a serious immigration problem in America,� Cruz said. “The American people understand that we must reverse the policies that invite criminals and terrorists to defy the law.�

Establishing himself firmly in the Donald Trump wing of the party on immigration, the Texas senator’s tough approach is an overt appeal to the billionaire mogul’s conservative supporters and, perhaps just as important, a chance to differentiate himself from rival candidate Sen. Marco Rubio of Florida.

The two have sparred for most of the week over immigration, which is quickly becoming one of the defining issues of the Republican field.

Rubio has tried to recover from being portrayed as too lenient on immigration for having supported a path to citizenship for immigrants who are in the U.S. illegally. Earlier this week, he suggested that Cruz has shared similar views on expanded visa and legalization programs.

Cruz, though, sought to put an end to any comparisons with Rubio on Friday by unveiling his own “stop illegal immigration� plan. It would beef up border security, halt the H-1B visa program popular in the tech industry and end citizenship for children born in the United States to parents in the country illegally, granted under the 14th Amendment to the Constitution.

No one would blame CBS News political director John Dickerson if he felt a little disappointed when he learned that Vice President Joe Biden decided against a run for the 2016 presidential nomination.

Had Biden decided to run, Saturday’s Democratic primary debate on CBS (6 p.m. Pacific) would have been his first on-stage confrontation with front-runner Hillary Rodham Clinton. It had the makings of a political battle royal.

Dickerson, who will moderate the debate at Drake University in Des Moines, agrees that Biden can liven up such events and even bring out clarity on the issues. But he also believes there is so much on the line for Clinton’s two remaining opponents, Sen. Bernie Sanders and former Maryland Gov. Martin O’Malley, they will need to come out swinging in their second debate if the primaries are to be competitive at all. And fights for survival generally make compelling television.

“They have to be more provocative because they don’t have any more chances,� he said over lunch Thursday at a Des Moines coffee spot. "And they should be. This is the one chance they have to engage. Where they can say, 'I disagree with you here -- I agree with you here.' Talk about the differences at the heart of the campaign. So they should do that regardless of where they are in the polls. That’s what these are about. They are not just stump speeches given in parallel.�

This time four years ago, most Republican presidential candidates had said little about their tax platforms, let alone gone out on a limb with anything dramatic. Not so in 2015.

Not only has nearly everyone in the GOP field already detailed their position on taxes, their plans are surprisingly bold, some even featuring ideas previously taboo to the party.

Sens. Ted Cruz (R-Texas) and Rand Paul (R-Ky.) are backing proposals for a European-style value-added tax, long a nonstarter in Republican circles, though both men are careful not to label it as such.

Sen. Marco Rubio (R-Fla.) wants to greatly increase child tax credits, and retired surgeon Ben Carson supports scrapping the sacred mortgage-interest deduction.

Most of the tax-cut plans would add to the deficit, but some, like Donald Trump's, are so large that even conservatives’ jaws drop.

“Woo, wow… they’re definitely pushing the envelope,� said Daniel J. Mitchell, a senior fellow at the libertarian Cato Institute.

Donald Trump dedicated nearly nine minutes of a 95-minute speech late Thursday to a rant questioning voters’ intelligence for listening to rival Republican presidential candidate Ben Carson. Trump told his audience in Fort Dodge, Iowa, that Carson’s claim in his biography that he overcame violent behaviors shows he is unstable.

And then Trump acted out his own rendition of the book’s anecdotes, including one in which Carson said he tried but failed to stab a friend. Carson wrote in his book that a belt buckle stopped the knife from penetrating. Trump stepped away from the podium to try to demonstrate that a belt can’t stop a knife.

"It moves this way, it moves that way!" Trump said of the knife Carson described. "How stupid are the people of Iowa? How stupid are the people of the country to believe this crap?"

The remarkable performance came after an interview with CNN in which Trump compared Carson’s description of his youthful anger as a pathological disease to the behavior of child molesters. Trump said a pathological disease is incurable, as are the behaviors of child molesters.

Trump continued ridiculing the “pathological temper� claim in Fort Dodge.

"This isn't something I'm saying — he's a pathological liar — I'm not saying it,� Trump said. “He said he's got pathological disease. He actually said 'pathological temper,' and then he defined it as 'disease,' so he said he has 'pathological disease.' Now if you're pathological, there's no cure for that, folks. OK? There's no cure for that."

Carson and Trump remain close in polls as lead GOP rivals. Although Trump was relatively subdued during Tuesday’s presidential debate in Milwaukee, the Republican has reupped his attacks on opponents.

"So that's who is in second place, and I don't get it," Trump said of Carson. "I don't get it."

Trump's comments drew attention Thursday night and Friday morning from the political world.

The Times' David Horsey offers an animated assessment of the candidates -- as dates.