NEW YORK — Today’s conventional wisdom is that Donald Trump’s best days are behind him and that his poll numbers will soon begin to descend. Maybe. But Trump has come to represent something fundamental about the Republican Party — the growing gap between its leaders and its political constituency. Even if he disappears, this gap is reshaping the GOP.

At the start, Trump’s campaign was based largely on his personality. On the issues, he had a grab bag of positions, lacking any coherence or consistency. But over time, like a good businessman, he seems to have studied his customers — the Republican electorate — and decided to give them what they want. And what they want is not what their party leaders stand for.

In a smart essay for Politico, Michael Lind argues that the modern Republican Party has built its ideology around three planks — economic conservatism, traditional social values, and hard-line foreign policy. The problem for the GOP is that in all three areas, its followers no longer believe in the party’s long-standing ideology.

If there is one belief that has united Republicans, it is that government is bad and bloated and that spending is out of control. The problem is that there are only two ways to significantly reduce the debt and deficits — raise taxes or cut Social Security and Medicare. Since the former is anathema to all Republicans — indeed, they want tax cuts — most conservatives propose paring down entitlement programs. That remains the centerpiece of House Speaker Paul Ryan’s appeal to conservatives. But the bulk of the Republican electorate is elderly, and increasingly making clear that they disagree.

The data on this is stunning. Lee Drutman points out that only 6.2 percent of the U.S. public favors decreasing Social Security — the rest think it should be kept at its current level or increased. A majority of Republicans believe it’s more important to maintain Social Security and Medicare benefits than to reduce the deficit.

Republican candidates have read the polling and begun adjusting their rhetoric. During the last presidential campaign, Ryan would often talk about entitlement reform. Today, few candidates mention it. Many use code language, and some — like Trump and Mike Huckabee — reject it outright.

This dilemma explains why Republican budgets feature huge gaps between revenues and expenditures. These budgets mirror the demands of the GOP electorate: smaller government, low taxes, but fully funded entitlement programs.

On immigration, which is in many ways a social issue, the divide between the elites and the rank and file has narrowed in recent years as leaders have realized that they cannot be seen as soft on undocumented immigrants. Those candidates who had more accommodating positions have reneged on them or sidestepped the subject when asked. Marco Rubio has done both: Since facing criticism from the right for helping write a bipartisan immigration reform bill in 2013, he has backed away from his position, and he avoided the immigration tussle Tuesday night.

Trump, on the other hand, knows that it is not possible to be too tough on the issue in the Republican primaries. Traditional GOP leaders like Jeb Bush and John Kasich have continued pushing an approach to immigration grounded in pragmatism and generosity, but the party is with Trump and Ted Cruz on the issue. Almost half think undocumented immigrants should be required to leave the country. A poll this week found that half of Republican voters think Trump is the presidential candidate best able to handle the immigration issue — almost five times the share any other candidate received.

The third plank, an interventionist foreign policy, is in some ways a legacy of the Cold War and was central to Ronald Reagan’s success. In its DNA, the Republican Party was historically more nationalist than internationalist, and isolationist rather than interventionist. It is returning to those roots. Over half of Republicans said in 2013 that the U.S. does too much to help solve world problems and should mind its own business.

Again, Trump gets it. He has increasingly favored nonintervention. He argues that we should not have intervened in Iraq and Libya and should not do much in Syria. He wants the Europeans to take the lead on confronting Russia over Ukraine. When asked by NBC’s Chuck Todd whether Ukraine should be a member of NATO, his answer was extraordinary and revealing: “Whether it goes in or doesn’t go in, I wouldn’t care.” I would wager that most Republicans would agree.

Trump has cannily exploited this gap between Republican voters and leaders. Perhaps a more charismatic politician like Marco Rubio or a clever conservative like Ted Cruz can somehow close it. But it’s more likely that these divides — that lie at the heart of the Republican Party’s ideology — will change its basic character.

Fareed Zakaria is a syndicated columnist. His email address is: comments@fareedzakaria.com.