Florida Senator Marco Rubio was riding a new wave of support on Thursday as the moderate Republican choice for presidential candidate.

His success in Iowa, coming in just behind conservative hardliner Ted Cruz and media sensation Donald Trump, had conservative donors contemplating throwing their support behind Rubio instead of Jeb Bush, once considered the most mainstream candidate.

The 62-year-old former Governor of Florida finished sixth in the Iowa Caucus, earning just under 3 percent of the vote, a full 20 points behind Rubio.

Often in such cases, a candidate will suspend his or her campaign and encourage benefactors to switch to a similar but viable hopeful. The Bush campaign has not taken that step in the hope that things could turn around in New Hampshire for the son and brother of two former presidents.

Rick Santorum, having abandoned his bid for the Republican nomination, lent his backing to Rubio instead.

Rivals converge on Rubio

Rubio's increased popularity, coupled with his apparent palatability in comparison with the more inflammatory Cruz, has also drawn other Republican candidates to increase their efforts against him. Besides one-time ally Bush, who has been hitting Rubio with attack ads for weeks, New Jersey Governor Chris Christie has been slamming Rubio on the campaign trail.

Christie called him a "a boy in a bubble," claiming he has done little since winning office in 2011, and adding that Rubio uses the same speech at every campaign event. Ohio Governor John Kasich has also questioned the first-term senator's credentials, saying that the country needs a more experienced commander-in-chief.

But voters appear not to mind, as Rubio's polling numbers continued to climb post-Iowa - including in the state of New Hampshire, which is the next state where primaries to determine each party's nominee will be held.

Republicans further to the right of Rubio have criticized the son of Cuban immigrants for his slightly more relaxed stance on immigration and abortion rights, but Rubio has still spoken of the need for more secure borders to curb illegal migration and identifies as pro-life.

es/gsw (AP, Reuters, AFP, dpa)