Few politicians have done more to block reform in Albany than State Senator Simcha Felder of the 17th District in Brooklyn. A Democrat, he has voted with Senate Republicans for years, giving them a one-seat majority since last spring that has let them obstruct legislation that could help clean up Albany and make the state a better, fairer place to live.

In Thursday’s primary election, Democrats can give their party’s nomination to a candidate who cares about their values: Blake Morris.

Mr. Morris, a lawyer who has been active in the community, has taken on the task of challenging Mr. Felder, who has worn the party’s label since he was first elected in 2012.

Mr. Felder has helped to stymie measures supported by a Democratic Assembly and a Democratic governor that would have strengthened tenants’ rights and women’s reproductive rights as well as mandated ethics reforms, voting reforms, campaign finance reforms, even speed cameras on streets around New York City schools.