(CNN) - A Democratic congressman from New York City who could face a competitive road to re-election this autumn is calling in a big gun.

And that big gun is former President Bill Clinton, who teams up at a campaign rally Friday morning with freshman Rep. Mike McMahon of New York's 13th congressional district.

The district covers Staten Island and a small portion of southwest Brooklyn, and is considered the most conservative in New York City. John McCain won the district by two points in the 2008 presidential election and George W. Bush carried it by 10 points in his 2004 re-election.

The district was held for a dozen years by Republican Rep. Vito Fossella, who decided against running for re-election two years ago after an extra-marital affair and a child out of wedlock were exposed following a drunk driving arrest.

The seat is considered the best chance of a GOP pickup in New York City. Of the top two non-partisan handicappers, the Cook Political Report rates the race as "lean Democrat" and the Rothenberg Political Report calls it "favored" for the Democrat.

McMahon, who voted against his party and the White House on health care reform, will face the winner of a two-candidate field in the September 14 GOP primary for the district.

Clinton teams up with McMahon at Wanger College. The former president is back on the campaign trail again next week, in his native Arkansas, when he's scheduled to appear at events for incumbent Democratic Sen. Blanche Lincoln and congressional candidate Chad Causey.

Clinton's become a "go to guy" this election cycle, helping out Democrats facing difficult contests. Last month he campaigned with Rep. Kendrick Meek in the days before Meek fended off a serious primary challenge for Florida's Democratic Senate nomination.

Earlier this year, Clinton was in Arkansas to help Lincoln win a bruising primary runoff election against the state's lieutenant governor. Lincoln now faces a very tough re-election battle in November against Republican Rep. John Boozman.

Clinton will also hit the campaign trail in June, when he teamed up with Mark Critz, the Democratic candidate in the special election to fill the late Democratic Rep. John Murtha's Pennsylvania seat. Critz ended up defeating Republican candidate Tim Burns.