Newly-minted presidential candidate Marco Rubio (R-Fla.) on Monday stressed that he will not simultaneously seek re-election to the U.S. Senate while running for president, saying that would "diminish your ability to succeed" -- indirectly taking a swipe at Kentucky Sen. Rand Paul, who is doing just that.

“If you’ve decided that you want to serve this country as its president, that’s what you should be running for. And I find myself in a situation where my Senate seat comes up for re-election at the exact same time as the presidency,” Rubio told NPR’s Steve Inskeep in an interview released Monday evening.

Florida campaign laws do not allow candidates to appear on a ballot for two different offices, which Rubio himself pointed out.

“To even be thinking about a Plan B in case this doesn’t work, I think diminishes your ability to succeed on the campaign because your mind will always be on: if this doesn’t work, then I could do something else,” he said.

Rubio didn’t mention any candidates by name. Then again, Kentucky Sen. Rand Paul is currently working to circumvent a similar law in Kentucky.

Despite what is shaping up to be a crowded — and potentially contentious — GOP presidential primary, the Florida senator wasn’t very keen on discussing his Republican rivals, instead aiming his criticism toward recently-announced Democratic candidate Hillary Clinton.

“As far as the Republican field is concerned, there will be plenty of time for comparison shopping. But on the Democratic side, I think Hillary Clinton is someone who is deeply wedded to the institutions of the 20th century,” he said. “Her plans are to spend more money on the existing higher education system. That system doesn’t work anymore.”

When asked whether his role negotiating a comprehensive immigration reform bill in the Senate – a measure he later distanced himself from – could hurt his presidential campaign odds, he again knocked Clinton.

“I’ve done more [on] immigration than Hillary Clinton ever did. I helped pass an immigration bill out of a Senate dominated by Democrats. That’s more than she’s ever done; she’s given speeches on it but she’s never done anything,” he said. "It didn’t work because at the end of the day we did not sufficiently address the issue of illegal immigration – and I warned about that throughout the process as well."

Rubio also insisted that the relationship between himself and former Florida governor Jeb Bush, whose own presidential election is all-but-certain, remains strong despite the likelihood that they will be competing against each other for the nomination.

“Jeb and I are friends and we’ll always be friends. I have tremendous admiration for him as a person, for what he did as governor and personal affection,” Rubio told NPR. “I’m not running against Jeb Bush and I’m not running against anybody in this field. I’m running because I strongly believe that I have something to offer this country that no one else in the field does at this moment in our history."