Manchester, N.H. - It was Donald Trump's first debate since he boycotted the Republican showdown in Iowa, but the spotlight Saturday was focused on two first-term senators who are perhaps his biggest threats to the GOP nomination.

Florida Sen. Marco Rubio and Texas Sen. Ted Cruz must have felt they had bullseyes on their chests throughout the debate at St. Anselm College in Manchester.

And the three mainstream governors, searching for a breakout moment after tepid showings in Iowa, had feisty performances at the senators' expense that gave their supporters reason to cheer.

Rubio was hit with attacks from New Jersey Gov. Chris Christie and former Florida Gov. Jeb Bush, both who painted him as too inexperienced to lead the country and compared him to President Barack Obama, also a senator elevated to the White House.

And Cruz was slammed by retired neurosurgeon Ben Carson for his campaign’s role in spreading inaccurate information at the Iowa caucuses claiming he was dropping out of the race. Trump also painted Cruz as a weak-kneed embodiment of Washington politics.

It was an undeniable sign that the rest of the Republican field sees the two senators as a rising threat ahead of Tuesday’s first-in-the-nation primary in New Hampshire.

It was also a chance for the mainstream candidates to make a final debate pitch to the state’s notoriously independent-minded voters. And Christie, in particular, seized at the chance to make a lasting impression as he took every opportunity to bruise Rubio.