The nearly unchecked powers of the president are controlled by the ideologues and special interests who dictate Republican nominations. Self-serving agendas take precedence over the selection of candidates with a record of abiding by the rule of law and the Constitution. Without urgent reforms, America will continue to succumb to what the Framers of the Constitution most feared — a populist tyranny.

Two consequential changes have brought us to this crossroads. The first: Control over nominations has shifted since the 1970s. Party officials committed to winning general elections with experienced candidates gave way to relatively small and ideologically unrepresentative segments of the electorate intent on advancing their narrow agendas. The relatively low turnout for direct primaries enabled evangelicals, members of the Christian right as well as virulent opponents of immigration, abortion, taxes, and government regulation to control the delegates to national conventions who select presidential candidates.

These changes overturned the Constitution’s design to “filter” the voice of the people and insulate elected officials, especially presidents. The Electoral College, Alexander Hamilton explained in 1788, was designed to produce “a constant probability of seeing the station filled by characters preeminent for ability and virtue” and preventing the selection of presidents inclined toward “cabal, intrigue, and corruption.”

President Trump is the nightmare. He won the 2016 nomination by scraping together less than 40 percent in early primary contests among a crowded field of opponents. As is typical of Republican primaries, three out of four voters identified as very or somewhat conservative and Trump won pluralities there. In contrast, about two-thirds of voters in the 2016 general election described themselves as moderate or liberal.

Trump’s open disregard for the rule of law and the Constitution was not a serious consideration for voters in the Republican primaries and the November general election. Nearly all Republicans robotically backed him in an era of intense party loyalty. A plurality of the remaining voters, including independents, were swayed largely by their reaction against Democrats: dislike of Hillary Clinton, opposition to the Obama administration, economic and cultural dissatisfaction and a desire for political change.

The second momentous change has been the expansion of presidential powers to act unilaterally in domestic and international affairs. Democrats and Republicans left a loaded gun in the Oval Office. With the onset of the Cold War, presidents routinely acted alone to send troops into real or potential conflicts, conduct assassinations abroad, and reach international agreements. Extreme abuses of power were mostly skirted by the vetting of political parties and their networks. They weeded out demagogues from the pool of presidential candidates and nominated, in most cases, candidates with a track record for governing effectively.

Then came Trump — a candidate propelled to the cusp of election by narrow ideological factions without the peer review of senior elected and party officials who are attentive to the rule of law. The result: imperial power is unmoored at a time that lacks protections against unqualified and unscrupulous presidents. Saving the republic now requires urgent reforms of the nomination process to filter out the demagogues that most worried the Constitution’s Framers. Changes are needed in both parties but most urgently in the Republican Party that lacks the informal checks from moderate donors and insiders.

A necessary starting point is to restore and expand the independence of unpledged Republican delegates: the national and state GOP leaders focused on protecting the party’s national reputation.

Until 2012, nearly a fifth of convention delegates were free to vote for any presidential candidate on the first ballot regardless of their state’s primary or caucus results. By 2016, the proportion of unpledged delegates was slashed to 6.9 percent and national and state party rules increasingly bound them to primary results.

Urgent reforms to restore balance to the Republican nomination process are possible but must be achieved soon. The party should maintain the central role of primary voters while also returning the ability of party leaders to create an off-ramp if activists favor a candidate who is a threat to rule of law and Constitution. Ideologues will throw up a predictable smoke screen, claiming that the reforms weaken democracy.

The truth is that primary voters will continue to dominate the selection of candidates. But in cases where activists are on the verge of imposing a candidate with extreme views about policy and the rule of law, party leaders must reserve a limited option to leverage their small fraction of delegates to tilt a convention toward alternatives better suited to our constitutional system and the views of most Americans. Unless immediate and vigorous action is taken, the nomination of another vengeful and unprincipled presidential candidate is a very real possibility in 2028.

Lawrence R. Jacobs is the Walter F. and Joan Mondale Chair for Political Studies and director of the Center for the Study of Politics and Governance at the University of Minnesota’s Humphrey School of Public Affairs. A member of the American Academy of Arts and Sciences, he has written or edited 19 books on American politics.