(Image Credit: Ethan Miller/Getty Images)

ABC News' Michael Falcone reports:

Mitt Romney's campaign is hoping that when Donald Trump calls, Michiganders will listen.

Trump has recorded a robo-call, paid for by the Romney campaign, which is highly critical of rival presidential candidate Rick Santorum.

"This is Donald Trump and I have to tell you that I'm tired of Rick Santorum pretending that he's some kind of DC outsider," Trump says on the call.

Trump dismisses the former Pennsylvania senator as a "career politician" who has "never had a job in the private sector." He accuses Santorum of working as a lobbyist before and after serving in Washington.

"Rick Santorum is completely entrenched in the Washington culture and he has been for decades," Trump says.

(Santorum worked for a law firm that lobbied on behalf of the World Wrestling Federation in the 1980's and worked as a consultant to several companies after he lost his re-election bid to the U.S. Senate in 2006.)

Trump, who endorsed Romney in Las Vegas in early February, has not appeared alongside the candidate since then. However, there are fresh signs that the Romney campaign is making strategic use of their celebrity endorser.

Trump joined Romney in New York City last week to make a round of fundraising and he has been hitting the airwaves for the former Massachusetts governor in Michigan. In an interview on WSGW in Saginaw on Monday Trump called Santorum a "Christmas gift" to Democrats.

"I don't think they believe it's going to happen," Trump said of the possibility that the Republican Party might nominate Santorum, "but boy, would they like it to happen because that would be an easy election."

On the robo-call, which will begin on Tuesday, Trump calls Romney an "outsider in the race" who "knows how to handle" China and OPEC - two of Trump's most-frequently cited international bogeymen.

"He's a good man, he's working hard" Trump says of Romney. "He will win. You've got to give him that chance."

Polls in Michigan had shown Santorum with a lead in Michigan, but a new NBC News-Marist College survey out on Wednesday indicated Romney has overtaken him. The poll gives Romney a narrow lead over Santorum, 37 percent to 35 percent with six days to go before voters head to the polls. Political observers point to the efforts of Trump, among other Romney surrogates, as one of the key reasons Romney is pulling ahead.

This is not the first time Trump has recorded a robo-call on behalf of a political candidate. He recorded one for Republican Congressional candidate Bob Turner in a New York special House election last year. Turner won.

"If Mr. Trump's robo-call has a similar effect as it did in the Bob Turner election," said Michael Cohen, special counsel to Trump, "I suspect that Governor Romney will be the victor in Michigan."