Sen. Marco Rubio said all of the things you’d expect in a TV interview explaining his decision to back Mitt Romney for president.

The Florida Republican said Romney offers “such a stark contrast” to President Barack Obama’s record, adding that “I have zero doubt in my mind that Mitt Romney will govern as a conservative.”

But it’s what else Rubio said during the interview on Fox’s “Hannity” that caught my attention. Rubio appeared to set about very purposely to shoot down the notion — currently being promoted by former Speaker Newt Gingrich (Ga.) and ex-Sen. Rick Santorum (Pa.) — that a contested or brokered nominating convention would be good for the Republican Party’s chances of defeating Obama on Nov. 6.

“I don’t have a problem with primaries. But I think we’re at a stage now where at least two of the candidates have openly admitted that the only way they’re going to be able to win the nomination is to have a floor fight in Tampa in August. And I don’t think there’s anything good about that. I mean, there’s no way that anyone can convince me that having a floor fight at the convention in Tampa in August is a recipe for victory in November. On the contrary, I think it’s a recipe for disaster. I just don’t think that’s a wise route to go. I think we’ve had a very good primary, I think all of the candidates have a lot to be proud of; I think it’s evidently and increasingly clear that Mitt Romney is going to be the Republican nominee.”

Some of my conservative Twitter followers seized on this as proof that Rubio’s endorsement was all mechanics and no passion for the candidate — a charge that Romney has at least partly earned. But Rubio tends to be quite articulate and careful about the words he chooses. He’s also the former Speaker of the Florida House, and as such, he thinks like a party leader.

Clearly he doesn’t have a problem with primary fights that appear to be uphill, having challenged and defeating a sitting governor in his Senate bid. But Rubio believes what many Congressional Republicans and professional GOP operatives know to be true, that a presidential nomination not determined until the late August convention in Tampa would in all likelihood hand a second term to Obama.

I wouldn’t be surprised if his purpose this evening was not only to endorse Romney at what he conceded to Sean Hannity was an advanced stage of the 2012 GOP primary, but to throw cold water on claims by Gingrich and Santorum that a contested convention would put the eventual nominee in a better position to defeat Obama.

Although Rubio’s endorsement and his explanation will surely anger some of his supporters in the conservative activist community, at least in the short term, the freshman Florida Senator tonight acted like a national party leader and showed that he intends to be a player, not just an agitator.

Also notable, Rubio did not explicitly rule out accepting an invitation to serve as Romney’s running mate, should one be extended.