Marco Rubio announced he’s running to keep his Senate seat Wednesday, saying he’s changed his mind about running in part because a Trump presidency is “worrisome.”

“The prospect of a Trump presidency is also worrisome to me,” Rubio said in a statement announcing his decision to run, after citing concerns about Trump’s opponent Hillary Clinton. “It is no secret that I have significant disagreements with Donald Trump. His positions on many key issues are still unknown. And some of his statements, especially about women and minorities, I find not just offensive but unacceptable. If he is elected, we will need Senators willing to encourage him in the right direction, and if necessary, stand up to him. I’ve proven a willingness to do both.”

“It is most important to act as a check and balance on the excesses of a president.” Rubio added.

Rubio’s choice to leak the story to the National Review is noteworthy, since the outlet is a strident opponent of presumptive Republican nominee Donald Trump, who defeated Rubio handily in his home state during the primary.