FOR MORE than two years, the Tea Party has driven our national politics. It gave full voice to anti-Obama anger. It framed last fall’s elections as a battle over spending and the growth of government. When its activists swept Republicans into power, the Tea Party established the contours of the current debate over deficits and reforming entitlement programs, which follow conservative principles much more closely than the Republicans’ limited formal power — they control only the House — should allow.

But last week, this tide seemed to peak, and then begin to roll back. Republican House leaders, having pushed through a budget written by Republican Representative Paul Ryan of Wisconsin that embodies the Tea Party ideal of a government drastically scaled back, suddenly flinched. They signaled that important components of the budget would not move ahead, in particular a plan to privatize Medicare. The chairman of the House Ways and Means Committee dismissed that idea flat out. John Boehner, the House speaker, provided cover. “It’s Paul’s idea,’’ he said. “Other people have other ideas.’’

This signifies something both important and under-appreciated, as meaningful as was the Tea Party’s rise. For all the attention and the soaring testimonies to the movement’s power, sending its representatives to Washington was only the first step. The true measure of its success was always going to be what effect these newcomers had on Republican leaders and the government they sought to change.

Now, an answer is coming into focus. The Tea Party may continue to alter races across the country, and could also shape the Republican presidential field. But it appears to have reached the limit of its influence in Washington. Here, where it counts most, the Tea Party is looking like a spent force.

There are a number of reasons for this. The outsized political personalities most closely associated with the movement have started to fade. Glenn Beck is waning. Sarah Palin’s presidential hopes are passing into rapid eclipse. Even Representative Michele Bachmann of Minnesota — founder of the congressional Tea Party caucus, heir to Palin, reliably batty provocateur, and once-proud supporter of the Ryan budget plan — has begun cautiously backing away.

She is doing so for the same reason as everybody else. The Tea Party message, so seductive in the abstract, can be deadly in its particulars to any politician seeking a broader appeal. As that doctrine is put into practice, even prospectively, voters are beginning to balk.

During the spring recess, for example, many Republicans went home to find angry constituents alarmed that they might lose their government benefits. In a special congressional election in two weeks in a conservative district in upstate New York, momentum appears to have swung to the Democratic challenger, who has mercilessly attacked the Republicans for supporting the Ryan plan. A recent USA Today/Gallup poll shows that Americans’ views of the Tea Party are growing more negative, with 47 percent unfavorable and just 33 percent positive. No wonder Republicans in Washington are having second thoughts.

Their retreat has not gone unnoticed. In Monday’s Washington Post, one frustrated Tea Party leader memorably assailed Boehner as “surrenderist.’’ But other Tea Party leaders (the grammatically creative and all the rest) are to some degree complicit in this slippage.

“They seem to have given up on holding the big rallies on [Capitol] Hill and fanned out across the country,’’ one top aide to a conservative congressman complained to me. “That’s too bad, because that is what was visible and effective in Washington.’’

It’s important to note that the Tea Party itself — its ethos, principles, and many committed activists — has not disappeared, and shows little sign of doing so. Rather, it has simply been impeded by a political reality that many of its members angrily reject. One possibility is that the movement could channel its frustration into the presidential primaries.

Another is that it could abandon the Republican Party. A new Gallup poll shows that 60 percent of Tea Party members would like to see a third party compete with Democrats and Republicans.

Most worrisome for Republicans is that these possibilities might merge and give rise to an independent presidential challenger. The Tea Party’s march on Washington may have stalled for now. But that doesn’t mean that it won’t reconnoiter and try again.

Joshua Green is senior editor of The Atlantic. His column appears regularly in the Globe.

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