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While the 6th District has plenty of intrigue, the state’s other seven House seats appear safely in hand for incumbents who likely will be heavy favorites in the November general election.

House Minority Whip Steny H. Hoyer, a Democrat, is expected to coast in the primary and likely will face the district’s GOP front-runner, state House Minority Leader Anthony J. O’Donnell.

Another notable GOP race will be in the 2nd District, where a field including state Sen. Nancy Jacobs, Delegate Richard K. Impallaria and Army veteran Larry Smith will vie to represent the party against Democratic Rep. C.A. Dutch Ruppersberger.

Aside from the 6th District race, the state’s most interesting campaign might be in the Senate, where political newcomers Daniel J. Bongino and Richard J. Douglas are in a tight race for the Republican nomination.

The winner likely will face the incumbent Mr. Cardin, who is hoping to hold off a Democratic primary challenge from state Sen. C. Anthony Muse.

“This is the sleeper race of the cycle. I assure you I would not have left my job if this race was unwinnable,” said Mr. Bongino, a former Secret Service agent. “People are ready for a change.”

The need for change has been a common talking point for both the GOP challengers and Mr. Muse, all of whom argue Mr. Cardin has grown insulated from the needs of Marylanders.

“People don’t want the same old, same old,” Mr. Muse said. “The fact that [incumbents] only show up at election time has been a major theme.”

Mr. Eberly said that Mr. Cardin will be very tough to beat in a primary or a general election, but that Tuesday’s results could be a good temperature gauge for Democrats’ mood in the state - particularly black Democrats.

If Mr. Muse, who is black, is able to get a substantial number of votes, Mr. Eberly said, it would indicate some discontent among black voters who might in turn prove reluctant to support Mr. Cardin in the general election or could vote against Democratic leaders on ballot initiatives this fall, including a proposal to legalize same-sex marriage.

“This will send a signal about what to look for in November,” Mr. Eberly said.