"I'm 100 percent," Santorum said Tuesday during an interview on Fox News's "On The Record," when asked if he was supporting or endorsing Trump. "That's endorse."

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The former Senator indicated a top reason for endorsing Trump is the vacant Supreme Court seat. Santorum said he made a couple suggestions for Trump's list of potential nominees

"The most important issue is preserving the Constitution of this country, and a liberal Supreme Court will destroy it," Santorum said.

Santorum echoed that sentiment in an email to supporters on Tuesday night distributed through his Patriot Voices email list, in which he discussed attending Justice Antonin Scalia's funeral in February.

"Over the past several weeks, I’ve had numerous conversations with senior members of the Trump Campaign, including a long heart-to-heart with Donald Trump," Santorum wrote, saying he was "incredibly encouraged" when Trump included some of his suggestions in a list of potential nominees.