THERE ARE two plausible explanations for the apparently lopsided race for the U.S. Senate seat in Maryland, in which the incumbent, Benjamin L. Cardin, seems to be gliding to reelection.

One is that Mr. Cardin, a Democrat elected in 2006, is a solid, substantive and serious lawmaker whose proven ability to cross partisan battle lines places him among the dwindling ranks of grown-ups in Congress. The other is the catatonic state of Maryland’s Republican Party, which, having once produced electable moderates like former governor Robert L. Ehrlich Jr. and former representative Connie Morella, has sunk into irrelevance.

Mr. Cardin — stolid, wonky, slightly rumpled — is no one’s idea of a political buzz machine. But he has been instrumental in Congress (including his 20 years in the House) in crafting legislation to promote job training, small business, health care and the Chesapeake Bay’s cleanup. Although his liberal voting record is firmly in the Democratic camp, he has seized opportunities at bipartisanship — most notably on retirement savings issues with Sen. Rob Portman (R-Ohio).

Mr. Cardin, co-chairman of the U.S. Helsinki Commission, which promotes democracy in former Soviet bloc countries, was also the key advocate in the Senate for legislation that would punish Russian officials involved in the death of Sergei Magnitsky, a lawyer who died in prison after exposing government corruption. Mr. Cardin pushed the bill through the Senate despite opposition from the Obama administration.

Mr. Cardin faces two main opponents. The Republican, Daniel Bongino, is a former Secret Service agent whose strident attacks on government and pledge never to raise taxes earned him the endorsement of Sarah Palin.

Mr. Bongino’s insistence that more tax cuts will not add to the deficit is theology masquerading as policy. His shrill attacks on Democrats and vows never to compromise on fiscal matters suggest he sees public office as a forum for ideological combat, not a means to get things done.

A third candidate, S. Rob Sobhani, has run twice in Republican primaries for the Senate but has mounted an independent candidacy this year. An affable businessman, he has advanced a set of half-baked policies: For example, he confidently predicts he will be able to attract billions of dollars to Maryland in investments from sovereign wealth funds. Given his candidacy’s lack of seriousness, it’s hard to understand why he is spending millions of dollars of his own funds on it.