AP Photo/Seth Wenig
Donald Trump, left, talks with former New York City Mayor Rudy Giuliani.
Giuliani told the New York Post, "I support Trump, I'm gonna vote for Trump," though he told Maggie Haberman of The New York Times he won't technically endorse Trump's candidacy. "He is a Manhattan convention delegate who can have more sway on the convention floor without formal endorsement," she explains.
Either way, it makes sense that Giuliani ended up in the Trump camp.
First of all, Giuliani's voters are the Trump base. Trump has a good shot at winning the New York primary with over 50% of the vote, and some of his strongest demographic groups are white Catholics, voters in the Northeast, and moderates. Trump drives conservative stalwarts nuts because he's not a consistent conservative; neither is Giuliani, and these voters aren't bothered by it.
But the biggest reason for Giuliani to back Trump is the same reason Chris Christie and Ben Carson found it worthwhile to endorse him, and that Newt Gingrich has been flirting with him: Trump offers, by far, the best opportunity for these people to wield power and shape policy in a Republican administration.
As I wrote last month when Carson endorsed Trump:
A normal candidate comes into a campaign with a huge entourage of operatives, allies, and experts - staffers from a Senate office or a gubernatorial administration, councils of policy experts advising a campaign, longtime political supporters, major donors. When you endorse a regular candidate like Sen. Ted Cruz of Texas, you're getting in line behind those people in the pursuit of power in the administration.
Trump has no such entourage. When Christie endorsed him, he became overnight Trump's most important political ally. He probably thinks the endorsement put him in excellent position to be vice president - or at least attorney general - and he's probably right.
Giuliani, like Christie, might want the attorney general job. But if Christie is Trump's running mate, they won't have to fight over it.