Financier John K. Delaney (D) and state Sen. David Brinkley (R-Frederick) officially entered the race for Rep. Roscoe Bartlett’s (R) seat Wednesday, ensuring competitive contests in both parties ahead of the April 3 primary elections.

Delaney joins state Sen. Rob Garagiola (Montgomery) in seeking the Democratic nomination, the same day former Montgomery County Council member Duchy Trachtenberg (D) said she could not follow through with plans to run because she faced a recurrence of breast cancer.

On the Republican side, Brinkley announced his plan to challenge Bartlett for their party’s nomination at an event Wednesday afternoon in Frederick.

Bartlett is running for an 11th term in the 6th district, which was altered under the state’s new congressional map by adding a slice of Democratic-leaning Montgomery County to the more conservative territory of Western Maryland.

Bartlett has never had trouble winning reelection, but both parties believe the new lines mean the seat is now up for grabs — likely the only genuinely competitive district in Maryland in 2012.

Delaney, who lives in Potomac, is the executive chairman of the Chevy Chase investment firm CapitalSource. He previously founded the commercial lending firm HealthCare Financial Partners, and he is also the founder of Blueprint Maryland, a nonprofit group that aims to create new jobs in the state.

In an interview, Delaney said he hoped his profile as a “proven job creator” and political novice will provide a useful contrast to Garagiola, who entered the race in November and quickly sought to lock up as much support as possible from the party establishment.

“I am NOT a political insider, and I embrace the notion that people, not party politics, choose a candidate,” Delaney said in a statement announcing his bid.

The 6th was drawn by Annapolis Democrats, led by state Senate President Thomas V. Mike Miller (Calvert), with Garagiola in mind, and he now has the public backing of multiple state senators as well as Lt. Gov. Anthony Brown and several other current and former elected officials.

But not everyone is backing Garagiola. Former Montgomery County Executive Douglas M. Duncan, who had considered running for the congressional seat himself, said early on that he was leaning toward supporting Delaney, in part because he thought there would be resentment in the district over the way it was gerrymandered for Garagiola’s benefit.

Unlike Delaney, Garagiola has raised money for campaigns before and has a head start in this one. But Delaney has considerable personal wealth, and he plans to use some of it to jumpstart his bid in a prohibitively expensive media market. Delaney said it was feasible that he could spend upward of $1 million from his own pocket.

A survey conducted for Delaney’s campaign in early November by the Garin-Hart-Yang Research Group found that 68 percent of likely Democratic primary voters were undecided in a contest between Garagiola, Delaney and Trachtenberg. The poll also found that none of the three Democrats were particularly well-known.

Milad Pooran, a doctor and member of the U.S. Air Force Medical Corps, is also running for the Democratic nomination.

Trachtenberg, meanwhile, said in a statement Wednesday that she was “facing a recurrence of an earlier illness.”

“I was diagnosed and treated for breast cancer earlier in 2011,” she said. “While I undertook the campaign with a clean bill of health, circumstances have now deteriorated to the point where I honestly cannot continue the race. I must focus my energies on treatment and recovery with the love and support of my family.”

The Republican side of the race is even more crowded. Bartlett, 85, has vowed to run for another term. But his chief of staff, Bud Otis, had to resign his post last month after it was reported publicly that he had been lining up support for his own bid in case Bartlett stepped aside.

That prompted Brinkley and state Republican party chairman Alex X. Mooney to announce exploratory committees for the Republican nomination. Perennial candidate Robin Ficker, businessman Brandon Rippeon, systems analyst Robert Coblentz and businessman Joe Krysztoforski are also running for the GOP nod.

Brinkley for his part, has already collected the endorsements of several prominent Republicans in the district, including state Sen. Chris Shank (Frederick) and Frederick City Mayor Randy McClement.

With the filing deadline for candidates looming Jan. 11, Mooney has yet to say whether he plans to launch a full-fledged campaign. “I’m still in the maybe category,” he told