U.S. Rep. Roscoe Bartlett faces his toughest fight in 20 years as he runs for re-election Tuesday in Maryland's newly redrawn 6th Congressional District, the Republican said Sunday.

Bartlett represents a solidly Western Maryland, Republican district. In 2010, the district had roughly 160,000 registered Democrats, 208,000 registered Republicans and 73,000 independent voters, according to the state Board of Elections.

But Tuesday's winner -- whether it's Bartlett or Democratic challenger John Delaney of Potomac -- will represent a district that has added a large swatch of liberal Montgomery County to the western counties, with roughly 193,000 registered Democrats, 146,000 registered Republicans and 94,000 unaffiliated voters.

"It's the toughest district we've ever run in," Bartlett said. "We're running as hard as we can, and what will be will be."

Though Bartlett won a Democratic district 20 years ago, it included largely Southern, conservative Democrats, Bartlett said. By contrast, "I suspect that many of the Democrats in Montgomery County you wouldn't say were all that conservative."

Political analysts say the state legislature included part of Montgomery specifically to replace Bartlett with a Democrat. The race has been such an uphill battle that national Republican party leaders have all but abandoned Bartlett, leaving him to fight on his own.

The election is going to hinge on getting Republicans in the traditionally blue state to the polls, said Bartlett's campaign manager, Ted Dacey, who was in Montgomery Village calling voters alongside his candidate and Republican volunteers Sunday.

But Democrats also warn that the race is going to be tight -- a "nail biter," said Delaney's wife, April.

Delaney, who lives just outside the district, faces a challenge in winning over Western Maryland, and volunteers like Frederick resident Waymon Wright described pushback when they made calls asking voters as far south as Frederick to support a Montgomery County Democrat.

More than 200 Delaney campaign workers knocked on doors Sunday, and more were in campaign offices in Hagerstown, Frederick and Gaithersburg making calls.

"My focus is just to cover as much ground across the district as possible," Delaney said during a visit with volunteers in Frederick. "We were in all five counties yesterday."