presidential candidate Donald Trump blasts Republican expected to endorse rival.

Republican presidential candidate Donald Trump assailed a leading committee chairman in Congress on Sunday for backing Marco Rubio, Trump's rival for the party's nomination.

Trump, the front-runner in the Republican race, needled Trey Gowdy for his role as chairman of the House of Representatives select committee investigating the 2012 attack in Benghazi, Libya, in which four Americans were killed.

In October, Hillary Clinton, 68, front-runner for the Democratic nomination, calmly deflected committee criticism of her handling of the attack while she was President Barack Obama's secretary of state.

"In total (the committee) was not good for Republicans and the country. I mean beyond Republicans, it was bad for the country. I hope he does a whole lot better for Marco," Trump, 69, said of Gowdy on Fox News' "Fox and Friends."

The conservative news site Townhall reported Gowdy's planned endorsement, and an email from the Rubio campaign confirmed that Gowdy, a South Carolina Republican, would travel with Rubio, 44, on the campaign trail on Tuesday and Wednesday.

"Marco is a rock solid conservative and a strong leader we can trust. I look forward to campaigning in Iowa with him, and introducing my good friend to voters across the state," Gowdy said in a statement.

A billionaire businessman and former reality TV star, Trump further needled Gowdy online, retweeting a number of messages critical of Gowdy and the committee.

"Face it, Trey Gowdy failed miserably on Benghazi. He allowed it to drag out and in the end, let Hillary get away with murder," one user wrote.

Despite Trump's critique, a Gowdy endorsement could boost Rubio, a U.S. senator from Florida who trails Trump in most national opinion polls but has been on the rise ahead of the first contest for the nomination, scheduled for Iowa on Feb. 1.

Rubio pulls 8.5 percent Republican support behind Trump's 39.3 percent, Ted Cruz's 12.8 percent and Ben Carson's 9.6 percent in a national rolling five-day Reuters/Ipsos survey issued on Dec. 24.