Rahm Emanuel's mayoral campaign released a new radio ad Friday featuring his old boss: the president of the United States.

The spot features snippets of President Obama's send-off speech when Emanuel stepped down as White House chief of staff to run for mayor of Chicago.

"When I first started assembling this administration, I knew we were about to face some of the most difficult years this country has seen in generations," the president says in the ad.

The ad also features Obama praising Emanuel's fitness as chief of staff.

"There was no candidate for the job of chief of staff who would meet the bill as well as Rahm Emanuel," Obama says. "This was a great sacrifice for Rahm, Amy and the family, to move out here. He has been a great friend of mine. He has been a selfless public servant, he has been an outstanding chief of staff."

And then Emanuel: "Thank you, Mr. President, for your warm friendship, your confidence and the opportunity to serve you and our country. I give you my word that even as I leave the White House I will never leave that spirit of service behind."

The ad featuring Obama, who remains popular in his hometown Chicago, could strengthen Emanuel's already formidable campaign.

On Thursday the Illinois Supreme Court overruled an appellate court ruling that Emanuel did not meet residency requirements to run for mayor, eliminating the biggest challenge of his campaign so far.

He has raised more money than his competitors, pulling in more than $10 million in the second half of 2010, and has maintained a double-digit lead in the polls. Former President Clinton, another former boss, stumped for Emanuel this month.

A recent We Ask America poll found Emanuel has the support of more than 50 percent of voters. If no candidate reaches that threshold, the top two candidates compete in a runoff.

Early voting starts Monday, and the election is Feb. 22.

Watch the ad here: