The endorsement of Mitt Romney by Florida Senator Marco Rubio signals the end of the Republican primary. He joins other tea party darlings, among them Utah Senator Mike Lee and South Carolina Senator Jim DeMint, in bowing to the inevitability of a Romney candidacy.

Rubio’s nod to Romney also follows on the heels of a string of party establishment (read rich guy) endorsements in recent weeks. These included the older George Bush and his son Jeb. But the Rubio nomination is especially meaningful. He is both a favorite of right wing anarchists and a rising star in the mainstream GOP. Rubio – along with Jeb Bush – is also thought to be the last best hope for saving the Republican Party from its knee-jerk tendency to alienate Latinos whenever the opportunity arises. He is a cross-constituency power player.

Both the Rubio and Jeb Bush endorsements were unusually tepid, though. Traditionally, endorsements are made before the endorser’s home state primary -- when they have the opportunity to affect the outcome. They are usually effusively positive.

But The Jeb Bush and Marco Rubio endorsements could only be described as tepid. Rubio essentially said he was endorsing Romney because the primary was hurting the party. Jeb’s endorsement was hardly more ringing, but at least he endorsed the candidate, not simply the end of a painful primary. Still neither of these guys stepped up when they should have, before the Florida primary.

Lukewarm endorsement or not, Rubio is right that the Republican primary is hurting the party’s chances. I wrote over a year ago that President Obama had no chance of being reelected. This election should have been a GOP cake walk. But boy, what a difference a year makes.

Gingrich-as-gadfly has been delivering stinging criticisms of Romney (on any subject) to anyone who would listen. His pronouncements are mostly notable for their apocalyptic construction, as if a Romney candidacy signals the end of life. But that’s Gingrich. He’s the perfect embodiment of “Please make it stop!” Party officials are thrilled that Newt’s owner, Sheldon Adelson, has declared his candidacy finished. Newt is now left to charge $50 for a photo with himself at his events. He may be out by tomorrow.

Santorum brings his own set of party-killing negatives, essentially serving as the focal point for the party’s antediluvian views on women, a woman’s place, and women’s health. He – along with help from a few state legislatures – has killed his party’s chances with women. Women voters now give Democrats (and President Obama) a 15 point advantage, largely owing to Santorum’s – and the party’s -- opposition to family planning.

So, dragged along by these fringe-thinkers, Romney’s favorability continues to drop. In five recent polls, his unfavorability is approaching majority. And his spreads are growing:

Meanwhile, President Obama finally has some wind at his back (despite rising gas prices.) The most recent ABC News Poll pegs his favorable number at 53%, ten points higher than his unfavorable number. That’s a 19 point advantage over Romney in favorability.

Nonetheless, Romney can still win the general election. In order to do so he needs:

• Effective RNC voter suppression in minority neighborhoods
• A successful campaign free of rich-guy gaffes
• A strategy to win back women
• A big negative ad campaign by Superpacs
• Marco Rubio as his vice-presidential mate

Yes, Romney needs Rubio on the ticket to win. It’ll be a cold day at the condom counter before Romney offers the vice-presidency to Santorum, or to Gingrich or to any of the other nutbag nominees. Jeb Bush won’t accept it. Neither Chris Christie nor Mitch Daniels delivers votes Romney wouldn’t already get. But Rubio can deliver the hopes and aspirations of the Latino community. Romney can’t win without a solid third of Latino votes.

Still, Rubio -- who has presidential aspirations of his own -- will only join the ticket if he believes Romney has a chance to win. That will be the true test of his endorsement.

Marco Rubio photo by Gage Skidmore