Rick Santorum decided to endorse Republican presidential candidate Marco Rubio after he ended his own bid for the White House on Wednesday. However, it appears the former Pennsylvania senator has no idea what Rubio accomplished as a U.S. senator.

After failing to gain traction in the 2016 race and finishing second-to-last in the Iowa caucuses on Monday, Santorum announced on Fox News that he is dropping out of the GOP primary election.

Santorum said he and his family decided the best way to achieve his campaign's goals was to drop out of the race and support a candidate who shares his values and has a better shot at winning the Republican nomination.

"We decided that we wanted to find a candidate that really espoused the values that we believed in, someone who really focused their campaign on trying to help ... those who are struggling on the margins," Santorum said during an appearance on "On the Record With Greta Van Susteren."

"That's why we decided to support Marco Rubio."

He went on to describe the Florida senator as a "new generation" leader and "someone that can bring this country together." Santorum also said Rubio -- who had a strong third-place finish in the Iowa caucuses -- is the best candidate to revive the middle class and combat ISIS.

However, despite praising Rubio as a natural "born leader" on Wednesday, Santorum fumbled when asked to name one of Rubio's accomplishments while serving as a Florida senator for the last five years during his appearance on MSNBC Thursday morning.

"Morning Joe" host Joe Scarborough repeatedly asked Santorum to name just one of Rubio's accomplishments, but he couldn't.

"He's been in the Senate for four years," Scarborough said.

"Can you name his top accomplishment in the Senate -- actually working in the Senate doing something that tilted your decision to Marco Rubio?"

"If you look at being in the minority in the United States Senate in a year when nothing got -- four years where nothing got done, I guess it's hard to say there are accomplishments," Santorum said in response.

"I mean, tell me what happened during that four years that was an accomplishment for anybody? It was complete gridlock."

Scarborough shot back that Republicans have controlled Congress for the past two years and asked what Rubio has achieved since being part of the majority.

"Joe, look, the Republicans have been in the majority for one year and one month, of which, as you know, he was running for president primarily," Santorum said. "The first four years he was in the minority, and nothing got done. And by the way, what happened this year under the Republicans?"

Scarborough continued to press Santorum, asking him to "list one accomplishment. Just one. Just one that Marco achieved. Maybe a bill that he wrote. Maybe a moment in a committee."

"OK, Marco Rubio was, No. 1, the speaker of the Florida House, which is not something that's a minor deal," Santorum said.

"I mean, he was elected by his colleagues to be the speaker of the House. No. 2, yeah, he spent four years in the United States Senate being frustrated like everybody else that nothing got done, and then you can't point to him and say well nothing got done and therefore he has no accomplishments."

Santorum went on to accuse Scarborough of making a "bogus" argument.

"It's actually not a bogus argument," Scarborough said.

"Let me ask the question one more time: List one accomplishment that Marco Rubio has achieved in four years in the United States Senate. It doesn't even have to be a passed bill."

"Well, I know he included something that went after the insurance companies in the most recent omnibus. I know that he fought for that to stop bailing out insurance companies," Santorum said.

"That's one thing that I'm familiar with that I just saw recently, but - and again, he was on the campaign trail and accomplished that.

"The bottom line is there isn't a whole lot of accomplishments, Joe, and I just don't think it's a fair question."

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