Rep. Roscoe G. Bartlett has defeated more challengers than he can count in his two decades in Congress.

But the odds are higher than ever that the latest contender could be his last, and Bartlett (R-Md.) knows it. Bartlett, 86, who is pushing for an 11th term in a newly redrawn district that gives Democrats a numerical edge, has been called one of America’s most vulnerable Republicans.

Since 1992, Bartlett’s quirky, down-home conservative style has been a good fit with Western Maryland. But it’s not his old turf anymore.

After the 2010 Census, Maryland lawmakers rejiggered boundaries to help the Democratic Party regain control of the U.S. House of Representatives by targeting Bartlett’s 6th District seat. Gone is a big chunk of his base of rural and exurban commuters in Frederick and Carroll counties. In their place are hundreds of thousands of new, mostly Democratic voters in Montgomery County. Bartlett said the district now has 185,000 Democrats, 139,000 Republicans and 79,000 independents.

“It’s an uphill fight, of course it is, because it was a gerrymandered district to make a Democrat pickup seat,” Bartlett said.

His opponent is newcomer John K. Delaney, the founder and chief executive of CapitalSource in Chevy Chase. Delaney has poured plenty of money and sweat into the race, and he has proven his tenacity with an upset victory over the primary candidate backed by party leaders.

Some Democrats say that fresh blood from their party will finally give the district a voice in Congress. Republicans say they think that the redrawn map was already the first step toward disenfranchising Western Maryland.

“The heart of it now has been shifted to Montgomery County. I think both the rural community and the urban community have been upset by this,” said state Sen. David R. Brinkley (R-Frederick).

Even Delaney dislikes the new map. But Delaney, along with many other Democrats, also hopes voters will look past the map to the people vying for office.

Bartlett’s résuméis an unusual farrago of achievements and interests. He has been a theological student, a doctoral recipient in human physiology, a homebuilder, a scientist, an engineer, an inventor, a medical school professor, a dairy farmer, a solar pioneer and a potential survivalist who keeps a well-stocked cabin in the mountains of West Virginia. With 10 children, 18 grandchildren and two great-grandchildren, he also qualifies as a patriarch.

His uncommon range of experiences allows him to find something in common with almost anyone, as Bartlett showed while campaigning in Gaithersburg last week.

At the Old Towne Cafe, he spoke with a couple about his early years in Montgomery, saying he had built his first house on a $600 lot on Muncaster Mill Road while attending college. When the couple talked about their concerns over health care, Bartlett shared his own, mentioning the needs of an autistic grandchild.

Down the street, at Wolfson’s Department Store, Bartlett reminisced with Mayor Sidney Katz, a Democrat, about rationing during World War II. (“You had to go get a chit to get a tire.”) At a dental office, Bartlett shared his thought that the Information Age is just a high-tech bubble. (“You can’t eat those electrons. They won’t keep the rain off your head. They won’t take you anywhere. They just help you do other things better.”)

At Winkler Automotive Service Center, he commiserated with its owner about traffic on Interstate 270 and the stresses of two-income families. (“This isn’t the politically correct thing to say, but when we drove the mother out of the home into the workplace and replaced her with the television set, that was not a good thing.”)

Bartlett describes himself as a traditional conservative, as reluctant to raise taxes and increase government spending as he would be to embark on foreign military ventures. He dislikes the federal health-care act and prefers tax-free health-care spending accounts. He thinks schools would reform if there were more competition and less federal involvement and went so far as to say that student loans are a slippery slope to the Holocaust. He later apologized for the remark.

A founding member of the Congressional Tea Party Caucus, Bartlett says he’s proud to be a GOP maverick: He opposed No Child Left Behind and the Troubled Asset Relief Program because he thought it was a bailout crafted for Wall Street at Main Street’s expense. “My party is sometimes wrong, and when they’re wrong, I’ll vote against them,” Bartlett said.

His shoulders are a bit stooped, he uses hearing aids and his gait is slow. But Bartlett, a member of the Seventh-day Adventists, showed a nimble mind that impressed Henry Abrahams, 77, after their discussion at the Old Towne Cafe.

“He’s interesting to talk to. Very knowledgeable,” Abrahams said.

Yet Bartlett’s campaign has been erratic about scheduling public appearances and coordinating coverage of them. “The reason they don’t see me is because I spend so much time fundraising,” Bartlett said.

But he is behind Delaney. Bartlett raised about $40,000 in a two-week period this month while Delaney raised more than $251,000, according to Federal Election Commission filings. Overall, Delaney has amassed $3.5 million, including $1.7 million from himself. Bartlett has pulled in almost $1.1 million.

As a newcomer, Delaney, 49, is busy introducing himself to voters. Well before sunup last week, Delaney shook hands with commuters at the Shady Grove Metro station while campaign staff let everyone know that he has the backing of The Washington Post’s editorial page and former president Bill Clinton.

“He’s surging at the right time,” Maryland Attorney General Douglas Gansler said while handing out Delaney brochures. “Look at this morning, how hard he’s working. People really believe, if you’re going to work for yourself, you’re going to work for them. And that’s certainly the case with John.”

Several commuters stopped to ask Delaney about his views. One was Tom Koval, 27, who lives in Derwood and works for the Department of Homeland Security.

“I gotta be honest — I’m leaning toward Roscoe Bartlett because I think the redistricting was kind of messed up, but I was hoping you can kind of change my mind,” Koval said.

“I do think the redistricting was messed up,” Delaney replied. “But, respectfully, I don’t think that should be the reason to vote for someone. You should vote for someone who’s going to do a better job for you going forward.”

Delaney is not new to politics: He gave more than $100,000 to the Democratic Party and raised more than $800,000 for Hillary Rodham Clinton’s failed 2008 presidential bid. But he has never run for office.

Although as a financier he’s in a line of work that might paint him as an out-of-touch plutocrat, Delaney reminds voters that he grew up in a modest home in Woodbridge, N.J. His mother was a homemaker; his father is still a member of the International Brotherhood of Electrical Workers. Delaney attended Columbia University on a union scholarship and then attended Georgetown’s law school before heading into business. Delaney is also a practicing Roman Catholic. He and his wife, April, have four daughters and live in Potomac.

By the time he reached his mid-40s he had created two highly profitable finance companies and taken them public. When he talks about the need to retool the U.S. economy, he sounds more like a businessman than a politician.

“Look it, I come from the real world where you have to work together to get things done,” Delaney said. “I think a lot people in politics come from a different perspective, where ideology rules and facts don’t really matter.”

He says the United States must become more competitive in a global economy by reforming its educational system, overhauling its immigration policies and laying the foundation for future growth by investing in infrastructure and developing plentiful new sources of clean energy. But he also calls for more public-private partnerships.

“I’m a big believer in the market,” he said. “The private sector creates the jobs. The government levels the playing field and creates the right incentives.”