"I have my own identity. I have my own positions on issues," Marco Rubio said. | Getty Rubio explains why he won't campaign for Trump

Sen. Marco Rubio (R-Fla.) is not campaigning with Donald Trump in the battleground state of Florida, but he says he has his reasons.

"It's not that I'm looking to undermine him, but I think the differences between us on key issues are so significant that I just don't plan to campaign — I've got to run my own race," Rubio told CNN in a live interview Wednesday.

Rubio announced earlier in the day that he had changed his mind and will seek reelection for his Senate seat, which he had previously said he would not do at the outset of his Republican presidential campaign. In explaining his reasoning behind not campaigning with Trump, Rubio said it had not changed from before he decided to seek reelection.

"I have my own identity," he continued. "I have my own positions on issues, and I'm not going to be out there undermining him or anything of that nature because I don't want Hillary to win, but I really think I need to tell people what I'm going to do as a senator as opposed to, kind of, and that was going to be the case irrespective of whether I ran."