Soon after he was elected, U.S. Rep. John Adler went back on the road.

He met with veterans, senior citizens, business owners, health-care providers and others in his South Jersey district. He also started "Congress on Your Corner," a program that takes him to libraries and diners to meet with constituents.

Adler, one of 40 first-year Democrats already targeted by Republicans in the mid-term 2010 election, has been hard at the kind of postelection campaign work that is a fact of life when you're a freshman - especially one from a politically mixed district.

"John Adler knew before he came into office that he would have to continue campaigning as soon as he took the oath," said David Wasserman, an analyst at the Cook Political Report. "One of the best ways a member of Congress can prepare for reelection is to do enough in the first months of a term to intimidate potential challengers."

In the fall, Adler became the first Democrat in memory to win in the Third District, which spans Ocean and Burlington Counties and includes his hometown of Cherry Hill in Camden County.

The Republicans have made it clear they will mount a strong challenge in 2010, with party leaders already firing off a couple of warning shots.

"The Republicans are going to target that district. It's inevitable," said political scientist Larry Sabato of the University of Virginia.

Adler won by 51 percent to 48 percent, taking Cherry Hill and the Burlington County side of the district. Though still a vote-rich area for Republicans, Burlington County Democrats took two freeholder seats last year as well. Ocean County remains a more Republican area.

Burlington County Republican chairman Bill Layton said his party hoped to unify around one candidate to avoid a costly primary, which some analysts believe hamstrung the GOP's ability to keep the seat last year.

But Adler is working round the clock, even sleeping in his Washington office on an air mattress some nights, to make sure he holds his seat.

Brushing aside questions about his political activities, Adler said he hadn't had much time for raw politics such as fund-raising.

"I want to do a good job," he said. "I found when I was in the state Senate that good government was the best politics."

After his swearing-in Jan. 6, he got two key committee appointments: Veterans Affairs and Financial Services. The first is especially important because his district, which contains the Joint Base McGuire-Dix-Lakehurst, has a high concentration of veterans and active military living in it.

The government work, however, will inevitably be mixed with the political.

Noting that there have been only two midterm elections in which the president's party didn't lose House seats, Sabato said, "There's going to be some snap back in 2010 for the Republicans to gain House seats."

Already, the National Republican Congressional Committee has sent out two news releases criticizing Adler, complaining that he had voted against term limits for committee chairs and voted on a stimulus bill.

Rutgers University's Ingrid Reed, director of the New Jersey Project, said 2010 would bring very different circumstances for Adler compared with 2008.

In the 2008 race, he ran with victorious presidential candidate Barack Obama at the head of the ticket, and the GOP was at war with itself.

In 2010, Adler will be running in an off year, when turnout is historically low.

"In New Jersey, that reverts to the kind of turnout which is like a legislative race and the faithful vote, and it looks like the majority of the faithful is still Republican," Reed said.

Even though dark political clouds may be gathering around him, Adler said of his first few weeks in office: "I'm giddy. Every time I walk past or through the Capitol, I get gleeful about the privilege of being in Congress."

Contact staff writer Cynthia Burton at 856-779-3858 or cburton@phillynews.com.