When Dan Donovan first ran for Congress three years ago, Rudy Giuliani was by his side. 

"Even if it were another Republican running against Dan, Dan would be the right choice," Giuliani said in 2015.

Now that Donovan is battling for his political career, the former mayor told NY1 he will show up for Donovan once again. 

"I know Michael Grimm as well, and I've endorsed him in the past. I believe Dan is entitled to re-election," Giuliani said. "He's proven himself to be an excellent congressman. He is the incumbent congressman. There is no reason to interrupt his service."

NY1 spoke with Giuliani by phone on Friday. He said Donovan deserves to get sent back to Washington. 

"Dan stepped in after Grimm had to resign," the former mayor said. "So I think Michael has to respect the fact that Dan changed his whole life around to represent the district. And if he's really concerned about the district, he needs to respect the job that Dan is doing."

The news of Giuliani's endorsement should not come as a surprise. The two attended a Yankees game in Washington earlier this week. But it still may be a big boost for Donovan, who is doing anything to try to show his support of the Trump administration. 

Giuliani is the president's lawyer. Giuliani told us he has not spoken to the president about the race. 

The former mayor says Donovan has done enough to show he supports Trump, a favorable position in the district. That's despite several votes he took earlier this year that were out of step with the White House, including voting against the tax cut. 

"When you say, 'Did he support the president enough?' I support the president. I'm his lawyer. However, if I were a congressman, my people would be better served if I voted what they needed, not just what the president needed," Giuliani said. "Sometimes there's a difference. Dan is capable of that. I don't know if Michael would be."

Wildly popular on Staten Island when he was mayor, Giuliani said he would be happy to come to the district to campaign for Donovan.

The Grimm camp told NY1 the endorsement wasn't a surprise. Grimm says Donovan needs all the help he can get.