After former Pennsylvania Sen. Rick Santorum dropped out of the Republican presidential race, he endorsed Marco Rubio for reasons apparently unknown to him or anyone else.

Santorum appeared on MSNBC's "Morning Joe" on Thursday, hours after throwing his support behind the Florida senator. The "Morning Joe" hosts repeatedly asked him to name a single one of Rubio's accomplishments, but Santorum came up short.

"Can you name his top accomplishment in the Senate, actually working in the Senate doing something that tilted your decision to Marco Rubio?" Joe Scarborough asked.

"You know, here's what I would say about that," Santorum said. "My feeling on Marco is someone who has tremendous potential, tremendous gifts. If you look at being a minority in the United States Senate in a year where nothing got -- four years where nothing got done, I guess it's hard to say there are accomplishments."

Scarborough pointed out that the Republicans have had the majority for more than a year and pushed Santorum to "list one accomplishment, just one, just one, that Marco achieved. Maybe a bill that he wrote. Maybe a moment in the committee."

After some back and forth, Santorum said that Rubio's top two accomplishments were being elected speaker of the Florida House of Representatives and becoming a senator. He later mentioned Rubio's efforts to undermine the Affordable Care Act by adding a provision into the Senate's latest spending bill to curb how much assistance insurance companies can get from the government.

All's not lost for Rubio, though. He finished third in this week's Iowa caucuses and is in second place among New Hampshire voters, who head to the polls next week. According to Politico, many figures in the so-called GOP establishment are shifting their support to him as well.