IN RECENT years, people have tended to ignore or even gently deride the deliberations of party platform committees. All these arguments over arcane questions of policy, and for what? The nominee, if elected, won’t be bound by any of it.

True enough. Yet the Republican decision this year to adopt no policy platform whatsoever shines a light on the democratic significance of the exercise — and the alarming vacuity of the Republican Party under President Trump. The Republicans are announcing that they stand for nothing. The party’s only reason for being is to gain and retain power for itself and its comparably unprincipled leader. What kind of future can there be for such a party? And how healthy can the two-party system be if one party has no principles?

Leading up to the Democratic convention last week, supporters of former vice president Joe Biden spent hours debating with supporters of some of the candidates he had beaten for the nomination, including Sen. Bernie Sanders (I-Vt.). They argued over health care, education funding, foreign affairs and more. They compromised at times, found new ground at times and hammered out a platform that the party could unite behind. If elected, Mr. Biden and Democrats in Congress won’t be bound by it, but the exercise will help shape their governing priorities. It was a useful democratic exercise.

The Republicans can’t risk such a debate. Many of the party’s senators and other leaders used to have principles, or at least claimed to. They believed in fiscal rectitude, free trade, limited executive power. Now, they have fallen in line behind a president who believes in none of that. So, are they the party of managed trade, unbridled presidential power, unlimited debt? No one wants to say that. Instead, they define themselves as the party of Donald J. Trump.

As a result, you will hear a great deal at their convention this week about what Republicans are against: socialism, the cancel culture, unbridled crime, Marxism, the “deep state” and — oh, did we mention socialism? At times, their negative passion will be focused on real but exaggerated problems (murder rates have climbed in some cities); at times, the threats will be imagined. And because they believe in nothing, they can put up no resistance when deranged and dangerous conspiracy-mongers move in, as has happened in several GOP congressional primaries.

You also will hear that they are for Mr. Trump’s “America first” agenda. But what is that agenda? No one dares spell it out, because he doesn’t know. One day he is a huge admirer of Chinese dictator Xi Jinping; a bit later, Mr. Xi is the source of all evil. In a cult of personality, no one can afford to be caught still saying nice things about Mr. Xi after the official line has changed. So better to say nothing at all.

And in a cult of personality, the government itself becomes the property of the leader. He wants to give his acceptance speech on the South Lawn of the White House? He wants to use the country’s chief diplomat, the secretary of state, as one more political prop?

The party can only cheer its approval.

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