WASHINGTON — When Prime Minister Benjamin Netanyahu of Israel came to the United States recently for another round of tense talks with the Obama administration, he got a decidedly warmer welcome from one of the rising Republican stars on Capitol Hill, Representative Eric Cantor, the incoming majority leader of the House.

But while Mr. Cantor and other newly empowered Republicans are eager to promote themselves as Israel’s staunchest defenders in Washington, the reconfigured American political landscape is a more complex and unpredictable backdrop for Middle East peacemaking.

Scores of Tea Party-backed candidates are entering Congress, many of whom favor isolationist policies and are determined to cut American foreign aid, regardless of its destination. Rand Paul, the newly elected Tea Party-backed senator from Kentucky, bluntly told the American Israeli Public Affairs Committee, an influential pro-Israel lobbying group, that they were going to disagree about the need for foreign aid and suggested that they move on to other topics, according to a person briefed on the meeting.

“One of the first things Congressman Cantor can do is to make sure that his colleagues vote for aid to Israel,” said Senator Charles E. Schumer, Democrat of New York, who also met with Mr. Netanyahu.