Marco Rubio and Ted Cruz: Hiccups, but High Points

There were stumbles: Mr. Rubio flubbed a line about parenthood. Mr. Cruz said he would eliminate five federal agencies and named four, citing the Department of Commerce twice.

But for the second consecutive debate, the young senators established themselves as effective masters of the format, culling from their stump speeches and staking out familiar turf with verve.

Mr. Cruz set off on extended riffs defending staunchly conservative positions on immigration and fiscal policy, and assailed Hillary Rodham Clinton as an embodiment of the “cronyism of Washington.”

Mr. Rubio laced his remarks with bits of his family’s story, flashing a boyish smile, and continued to project a relative fluency on matters of foreign policy.

Donald J. Trump: An Attack Dog, but a Sleepy One

The formula is now well-established: Punch down at lower-polling rivals, recede when the conversation wades too deep into the policy thickets.

Though Mr. Trump began the evening subdued, by his standards, he quickly found his way to targets new and old: Gov. John Kasich (“I don’t have to hear from this man”) and Carly Fiorina (“Why does she keep interrupting everybody?”), among others.

But opponents like Mr. Kasich and Jeb Bush forcefully dismissed Mr. Trump's immigration proposals (border walls, mass deportation) as unrealistic and damaging to the Republican brand. And when details were required on other policy matters, Mr. Trump often equivocated, faded or both.

Jeb Bush: Better. Maybe.

Mr. Bush has seemingly ached for a breakthrough for several debates. It is not clear he found one.

Still, there were signs of improvement. After receiving scant speaking time two weeks ago, Mr. Bush butted in early and sarcastically thanked Mr. Trump for telling Mr. Kasich to cede the floor.

Mr. Bush then derided Mr. Trump’s immigration plan. Later, he criticized Mr. Trump’s suggestion that Russia could be trusted to “knock the hell out of ISIS,” likening the position to a “board game” mentality.

In a break from the last debate, though, Mr. Bush avoided another sharp showdown with Mr. Rubio, who bested him last time.

Ben Carson: Effectively Forgettable

He had a wholly unremarkable night. Perfect.

At a moment of intense scrutiny after a series of news reports questioning elements of his biography, Mr. Carson came away largely unscathed. Pressed on the reports, he said, “I have no problem with being vetted. What I do have a problem with is being lied about.”

He then pivoted, to cheers, to an attack on Hillary Rodham Clinton’s honesty concerning the Benghazi, Libya, attack. There was no further follow-up on his own credibility, from either the moderators or his competitors.

Separately, Mr. Carson said he opposed raising the minimum wage, after previously expressing an openness to the idea.

Rand Paul: Still Here

Mr. Paul reminded voters that on some central issues, he stands alone in the Republican field, arguing against overzealous military spending.

Shouting “Marco! Marco!” in a memorable exchange with Mr. Rubio, Mr. Paul said it was not conservative to “keep promoting new programs that you’re not going to pay for.”

He also got the better of Mr. Trump, who had discussed at length China’s purported role concerning the Trans-Pacific Partnership. “We might want to point out,” Mr. Paul interjected, “China is not part of this deal.”