Voters on Roosevelt Island and Manhattan’s Upper East Side go to the polls this morning in a special election for state assembly, and we urge a vote for Gregory Camp. Mr. Camp, who favors gay marriage, rent stabilization, and abortion rights, and who opposes the death penalty, may be the most left-wing candidate ever endorsed by The New York Sun. He is also endorsed by Mayor Bloomberg, Citizens Union, and the New York Times.

But during an election-eve visit to our newsroom yesterday, he offered an intelligent, thoughtful discussion of his support for tax simplification, strong national defense, and a DNA law that would help solve more crimes by collecting DNA samples from all criminals.

Electing Mr. Camp, a Republican, to the Assembly would help erode, if only by one vote, the Democratic majority of Assembly Speaker Sheldon Silver, who is sometimes an obstacle to progress in Albany. Mr. Camp, who holds both a law degree and business degree from Yale, has experience both on Wall Street and in law enforcement. He worked as a prosecutor for the district attorney of New York County, Robert Morgenthau, and on criminal justice issues in the Pataki administration.

More broadly, one-party government is never healthy for democracy, and at the moment, every local elected official other than the mayor from Manhattan is a Democrat. It’s “not healthy for the debate,” Mr. Camp says. That’s an understatement. Voters can help turn things around by supporting him in today’s election. A victory would be a step toward restoring a two-party system in New York.