WASHINGTON — U.S. Rep. Conor Lamb is on a winning streak.

The moderate Democrat from western Pennsylvania’s 17th Congressional District has proven himself to be an adept politician — winning not just one, but two, competitive U.S. House elections in 2018.

He didn’t do it by excoriating President Donald Trump or promising to push a liberal agenda in the U.S. House. He’s a Marine and former federal prosecutor who calls the Affordable Care Act a flawed bill, welcomes natural gas extraction, and ran a campaign ad featuring him wielding a rifle.

Now, Lamb is walking a fine line on Capitol Hill as he represents a district that backed Trump within a party that’s focused on ousting the president in 2020. Republicans, meanwhile, are eyeing his seat for a pickup in the next congressional election.

While some of his colleagues are getting behind ambitious policy proposals like the Green New Deal and Medicare for All, Lamb appears to be seeking middle ground — a tactic that’s become less common lately in a deeply polarized Congress.

“He’s going to be cautious and not jump into a very progressive agenda, there’s just no doubt about that, because it’s the nature of his district,” said G. Terry Madonna, director of the Center for Politics and Public Affairs at Franklin and Marshall College.

Lamb told CNN in November that he’s not interested in seeing the president’s tax returns and he doesn’t support impeaching Trump, both of which are top priorities for some of his colleagues. “I want to build infrastructure and get prescription drug prices down,” Lamb said at the time.

Speaking at the University of Pennsylvania last month, Lamb called the concept of the Democrats’ Green New Deal plan to combat climate change “fine.”

But, he said, “Where I come from, people are a little more practical and pragmatic. They want to know how things like this are going to affect our jobs and how is this going to affect our energy bills,” according to the Daily Pennsylvanian. “It doesn’t really address any of those things.”

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Lamb’s 17th District seat, west of Pittsburgh, encompasses suburbs in Beaver County and parts of Allegheny County, and Butler County. The new district, created when Pennsylvania’s Supreme Court redrew the map last year, voted for Trump by 2.5 percentage points in 2016.

Lamb won the seat comfortably in November against former Republican Rep. Keith Rothfus. He had just come off a narrow win in an April special election to represent what was then the 18th District, where Trump won by about 20 percentage points in 2016.

Republicans see the district as a prime 2020 pickup opportunity.

The National Republican Congressional Committee included Lamb on its initial list of 55 offensive targets in 2020.

“I think Conor Lamb is very vulnerable because of the way the Democratic Party has behaved so far,” NRCC spokesman Michael McAdams said in an interview. “He’s got to be very uncomfortable that he’s got to own all these socialist policies.”

McAdams pointed to the Green New Deal and Medicare for all as Democratic policies that won’t play well in Lamb’s district, even if he doesn’t support them personally.

It will be difficult for Lamb to distance himself “in a Democratic party that’s dominated by socialists,” McAdams said.

Madonna, of Franklin and Marshall College, expects Lamb to seek exposure as a member of Congress, but he’ll want to be “careful how he gets the attention.”

He’ll be “wary of moving too far to the left,” Madonna added, and “I think he’s going to separate from his party as much as he has to, whatever that happens to mean.”

Some political experts who track national House races think Lamb has a safe seat — at least for a while.

“I’m skeptical that Conor Lamb is going to lose in 2020,” said Nathan Gonzales, editor and publisher of the newsletter Inside Elections. “He ran an impressive campaign in the special election” and “destroyed” a Republican member of Congress in the November race.

Gonzales said Lamb has been able to define himself as “being his own type of Democrat,” although there’s a risk over time that he’ll get lumped in with the national party because the more liberal voices tend to get the most attention.

Dave Wasserman, who tracks House races for the Cook Political Report, called the Pennsylvania map released in 2018 “tailor-made” for Lamb.

“All in all, this was a district that was perfectly suited for him, and it shouldn’t be too difficult for him to keep the seat in 2020,” Wasserman said. “The main challenge for Lamb is the next redistricting cycle.”

His 2020 race could also be impacted by the Democrat at the top of the ticket in 2020.

McAdams of the NRCC said that more liberal candidates in the mix so far — like U.S. Sen. Kamala Harris of California and U.S. Sen. Bernie Sanders of Vermont — “are not good people for Conor Lamb.”

Lamb called former Vice President Joe Biden his early favorite to get the nomination during his speech at the University of Pennsylvania.

“There are some who just clearly get it in terms of union rights, jobs, concerns of elderly people,” Lamb said. “I’ll be listening.”