Ahead of Tuesday's Maryland primary, state Sen. Rob Garagiola (D) talks with Melanie Jackson, an elementary school teacher at Cedar Grove Elementary, as he campaigned door to door in Germantown. (SUSAN BIDDLE/FOR THE WASHINGTON POST)

A story that began months ago in the map-drawing rooms of Annapolis is nearing a crucial plot twist, as one Democrat is set to claim the party’s nod for November in the lone Maryland congressional district with a realistic chance of changing hands this year.

The contests for the Democratic and Republican nominations in the reshaped district held by Rep. Roscoe G. Bartlett (R) are the main local attractions Tuesday, as Maryland voters will cast their ballots in a host of congressional races and the Republican presidential primary. Candidates have spent the frantic final days knocking on doors, shaking hands and making last rounds of phone calls seeking votes.

In Bartlett’s district, which now includes the western portion of Democratic-leaning Montgomery County and the Maryland panhandle, the incumbent is trying to fend off primary challenges from state Sen. David R. Brinkley (Frederick), Del. Kathy Afzali (Frederick) and a handful of other hopefuls. State Senate Majority Leader Robert J. Garagiola (Montgomery) and financier John Delaney are locked in an expensive and heated contest for the Democratic ballot line, with Air Force doctor Milad Pooran, among a group of other candidates, trying to nudge into the top tier.

Sen. Benjamin L. Cardin (D) also faces an intraparty contest, as state Sen. C. Anthony Muse (Prince George’s) is looking to unseat him in the primary, while former Secret Service agent Daniel Bongino and ex-Defense Department official Richard Douglas have been the most active Republican candidates. Cardin is considered the favorite, both against Muse on Tuesday and against the GOP nominee in the fall.

Aside from Bartlett, the state’s other seven incumbent U.S. House members are all expected to keep their seats in November.

Over the weekend, Delaney and Garagiola crisscrossed Maryland’s 6th Congressional District, seeking to drive home the same messages they had for months. Delaney portrayed himself as a reform-oriented newcomer who has drawn the backing of former president Bill Clinton. Garagiola emphasized his record in Annapolis and support from local unions and progressive groups.

On Saturday, Garagiola spent the afternoon knocking on townhouse doors in the Waters Landing community in Germantown. Although anger toward office-holders may be strong nationally this year, Garagiola said residents — particularly Democratic primary voters — in this district were different, since so many of them work for or are dependent on the federal government for their livelihoods.

“They understand what goes on [in government], and I think many are happy with the direction the state’s going,” Garagiola said. “We’ve done some good things since I’ve been in office. How can you argue with having the best schools in the country four years in a row?”

Doug Rowland, 39, a federal government employee, said he was “definitely interested” in voting for Garagiola because he supports “a progressive tax code and investment in education.” Delaney’s platform was also attractive, Rowland said, “but he doesn’t have the background and experience we’re looking for.”

Garagiola was the early favorite in the contest, with the backing of much of the state Democratic establishment behind him and district lines drawn to be favorable to him.

But Delaney, the founder of the Chevy Chase commercial lending firm CapitalSource, has outspent Garagiola by a wide margin, both by raising more campaign cash and by putting in at least $1.4 million from his own pocket. Having flooded the district with mail and advertising, Delaney released two internal polls last week showing him with a wide lead over Garagiola.

Garagiola’s camp is skeptical of those numbers, particularly given that such groups as the League of Conservation Voters and all the major unions are backing him and putting grass-roots resources into getting the vote out Tuesday.

“Our local union has said really good things about him, and he was the recommended vote,” said Melanie Jackson, 30, an elementary school music teacher who lives in Waters Landing. “I pretty much listen to our union.”

As he greeted commuters at the Frederick MARC station Friday afternoon, Delaney said he’s often been asked, “Are you currently a politician?” He sees the frequency of that question as reflecting poorly on Garagiola’s chances Tuesday and on Bartlett’s chances in November.

Bishop Smith, who lives in Frederick and works at Wal-Mart, said that he had yet to decide his vote but that “it will probably be for Delaney.” Smith said Delaney seemed “trustworthy” and committed to “work for the middle class.”

Pooran, who also stopped at the Frederick MARC station Friday, predicted a low turnout because of the negative tenor of the race, mainly between Garagiola and Delaney.

“People are very frustrated by that,” Pooran said. “They thought, ‘This is finally our chance to have a Democratic candidate that we can be proud of, and all we’re getting is two guys that are going after each other.’ ”

On the Republican side, Brinkley went on the air with an ad last week asking whether the country is better off now than when Bartlett took office 20 years ago, and his campaign said Saturday that the race was a “virtual dead heat” between him and Bartlett. But Bartlett appears to be in strong position to hold on Tuesday, as Brinkley, Afzali and five other challengers are likely to divvy up the anti-incumbent vote.