Get ready for a long fight

In recent years, the Democrats and Republicans have battled along a liberal-conservative axis of conflict that emphasizes disagreement over the size and scope of government rather than divisive disputes about racial identity. During the 2008 and 2012 presidential elections, for instance, John McCain and Mr. Romney ran against Mr. Obama’s domestic policy proposals on issues like health care and the economy.

After 2012, the Republican Party hoped to continue along this path and expand its appeal to young people, minorities and women. But as the political scientists Gary Miller and Norm Schofield note, candidates and parties sometimes “engage in flanking moves so as to enlist coalitions of disaffected voters.” By changing positions on social issues that cut across party lines, they seek to attract voters who are only loosely attached to the other party.

Mr. Trump seems to have pulled off one of these maneuvers in shifting from traditional conservatism to a kind of race-inflected nationalism. Though the move cost him votes among college-educated whites, he attracted support among the larger group of whites without a college degree (a substantial minority of whom had backed Mr. Obama in 2012), pulling in just enough votes in the Rust Belt to tip the election.

Despite all the attention paid to economic anxiety as the basis for Mr. Trump’s appeal, the evidence to date is more consistent with his brand of identity politics being the most important cause of this shift in voting patterns from 2012 (though of course economic anxiety and group animus are not mutually exclusive).

Mr. Trump’s approach has the potential to transform the party system. First, the success of his campaign may encourage other Republicans to adopt his model. He has shown that the penalty for deviating from orthodox policies is minimal and that an ethno-nationalist style can have significant electoral advantages.

Second, though presidents cannot impose their will on most of domestic policy, they can help define the issues on the political agenda. In the choices that he makes, Mr. Trump may play down conflict over the size and scope of government and shift the political debate toward questions of national identity, immigration and culture.

Finally, few Republicans are likely to want to cross Mr. Trump and his energized supporters given the threat of a potential primary challenge in 2018.

Consider, for instance, Mr. Trump’s decision to name as his chief strategist Steve Bannon, the head of Breitbart, a website described in an article in the conservative National Review as catering to “a small but vocal fringe of white supremacists, anti-Semites and internet trolls.” Though the move lacked recent precedent, no Republicans in Congress objected, which made the issue into a partisan dispute with Democrats. Mr. Trump has also stirred emotions by promising to deport two to three million undocumented immigrants. By contrast, the fate of a tax cut — normally the top G.O.P. domestic policy priority — has received less attention (though the party will almost certainly pursue one).

Mr. Trump’s success is likely to provoke a response from Democrats that could accelerate this shift. They face an outraged liberal base that is likely to reject conciliatory messages intended to win back votes among the white working class.

The party might instead double down on cosmopolitan appeals to the minority voters and college-educated white voters who were the main target of Hillary Clinton’s campaign. The strategy failed in 2016, but the incentive to try again is clear. Democrats came closer to winning several Sun Belt states where minority and college-educated white populations are growing, like Arizona and Georgia, than they did some traditional Midwest strongholds with higher numbers of noncollege whites, like Ohio and Iowa.

A focus on cosmopolitanism might make electoral sense for Democrats given the changing demographics of the country, but it could further weaken their appeal to whites without college degrees, dividing the electorate by race and class even more.