Republicans have put his face in their campaign commercials and spat his name as an insult on the debate stage. Presidential candidates and talk-radio hosts have invoked him as a kind of comic-book villain, thwarting Republicans at every turn.

Senator Chuck Schumer, Democrat of New York, has become the anointed target of Republican wrath.

For Mr. Schumer, it reflects a new stage in his career: Over the course of his four decades in politics, Mr. Schumer has steadily transformed himself from an overeager Brooklyn congressman and cable-television personality into one of his party’s chief political strategists and a powerful Washington deal maker. He is expected to take over as the Senate Democratic leader this year, after Senator Harry Reid of Nevada retires.

But Republicans say Mr. Schumer’s ballooning place in the conservative imagination is about more than his anticipated promotion.

He is increasingly seen as an avatar of Democratic craftiness and frustrated conservative aspirations: a wily tactician who has routinely defanged his Republican adversaries with ease, first as chairman of the Democratic Senatorial Campaign Committee and more recently as a lead negotiator on the issue of immigration reform.