Marco Rubio campaigns in Siouxland

Ted Cruz at 18.6 percent and Trump at 35.6 percent, according to a RealClearPolitics averaging of polls. I'm gonna tell you why. They are saying that Rubio isn't a conservative, therefore Gowdy isn't a conservative because of his endorsement. "I hope he does a whole lot better for Marco", Trump, 69, said of Gowdy on Fox News' "Fox and Friends".

Gowdy of SC, who sits on the House of Representatives Oversight Committee, announced his support for the junior senator from Florida while on a two-day campaign swing with the candidate through Iowa.

"Usually, I don't think endorsements mean a great deal, but this is an exception", said David Woodard, a Clemson University political science professor who has worked on Gowdy's campaign in the past.

"Marco is a rock solid conservative and a strong leader we can trust", Gowdy said in a statement to reporters prior to Monday's formal endorsement.

Rep. Trey Gowdy, a South Carolina Republican, endorsed Marco Rubio on Tuesday during a campaign stop in Iowa.

Politico reported Gowdy also appeared at a campaign event with Rubio on Tuesday. "He allowed it to drag out and in the end, let Hillary get away with murder", one user wrote.

Rubio has steadily climbed in the GOP primary polls, reaching second place in early December behind frontrunner Donald Trump.