Enough with the indignant press releases, strongly worded emails, disapproving tweets and mournful cable television appearances.

Republicans in Congress need to realize that they are not merely constitutional potted plants. Despite mantras of impotence, the elected members of the party need to remember that they have the power to pressure the White House. And they can do it without derailing a conservative agenda.

At that news conference in Helsinki, the world was confronted with an extraordinary stew of narcissism, appeasement, moral surrender and the chronic dishonesty that Republicans have been willing to tolerate for so long. But now the stakes are higher.

In just a few days, President Trump undermined the global world order, weakened our alliances, cast doubt on our commitments to NATO, sided with Vladimir Putin over our own intelligence agencies and suggested that the Russians be allowed to interrogate a former ambassador to their country. Despite the attempted walkbacks, clarifications and various obfuscations about dropped contractions, the damage is real. And now Mr. Trump wants Mr. Putin to come to Washington.

The danger should be obvious. That’s why mere expressions of outrage simply are no longer adequate.

It is precisely moments like this that the author of Federalist 51, generally thought to be James Madison, had in mind when he explained our system of checks and balances: “Ambition must be made to counteract ambition. The interest of the man must be connected with the constitutional rights of the place. It may be a reflection on human nature, that such devices should be necessary to control the abuses of government.”

Let’s be honest: Most Republicans have been too afraid of the president’s tweets to rise to the occasion. Their reluctance is understandable: In one poll, 79 percent of Republican voters said they were just fine with Mr. Trump’s performance in Helsinki. Breaking too decisively with the president risks offending the base and perhaps inviting a primary challenge. The end of the political careers of Senators Jeff Flake and Bob Corker and the defeat of Representative Mark Sanford are cautionary tales for many Republicans.

So Republicans who privately bemoan the president’s recklessness are content to rationalize, wring their hands and do nothing. But now they need to look past his tweets and even their own electoral base to the larger question of their constitutional responsibilities. Republican members of Congress need to act like a political party with principles rather than outsourcing their consciences to a handful of critics who are willing to say out loud what many of them are saying in private.

Taking action now is not merely a matter of recovering political courage and integrity; it would also be a fundamental reassertion of Congress’s Article I powers and our system of checks and balances. It also might save the political reputations of members of Congress who risk becoming footnotes for their complicity in Mr. Trump’s march of folly.

“The dam is finally breaking. Thankfully,” tweeted Senator Corker, who heads the Senate Foreign Relations Committee. But it will break only if he and his colleagues actually do something.

Mr. Corker, for example, sits in the chair once held by such giants of the Senate as Henry Cabot Lodge, William Fulbright, Arthur Vandenberg and Frank Church, who famously used their power (not always wisely) to challenge the policies of the executive branch. They also remind us that senators can wield authority even when they are not legislating. In the 1930s, the Democratic chairman of the Senate Judiciary Committee, Henry F. Ashurst, effectively killed Franklin Roosevelt’s court-packing scheme by delaying hearings.

If appealing to history is insufficient, how about a look at the polls?

This may be the Republicans’ last chance to persuade voters that a Republican Congress can be trusted to hold the president accountable. Although Republican voters are sticking with the president, an analysis of results from a recent NBC News-Wall Street Journal poll found that more than half of the voters in competitive House districts prefer candidates who promise to be a check on Mr. Trump.

So what would it take to check this president?

Given the Republican Party’s thin majority, any two of its senators can effectively bring the Senate to a halt, blocking nominations and legislation. It may come to that, but collective action would be more effective.

Congress could pass a resolution like the one co-sponsored by Senators Flake of Arizona and Chris Coons, Democrat of Delaware, reaffirming the intelligence community’s finding of Russian meddling in the 2016 election, commending the Justice Department for its investigation and making it clear that the Russian Federation should be held accountable.

As the editors of The Weekly Standard suggested last week, Congress could pass a resolution of censure for the president’s conduct and his subsequent comments. Congress can also take steps with concrete consequences:

• Pass legislation imposing new sanctions on Russia in the event of any future attacks on our democratic process. Dare President Trump to veto it. Override him if he does.

• Hold hearings that would include in-depth testimony from the national security team on the Russian attacks, putting the case on the record (again), while putting pressure on members of the administration to correct the president’s comments. Similar hearings should focus on our commitments to NATO.

• Take up legislation that would protect the special counsel, Robert Mueller, from Mr. Trump. That bill has already been approved by the Senate Judiciary Committee with bipartisan support but has been blocked by the Senate majority leader, Mitch McConnell.

• Pass legislation that would limit President Trump’s power to impose unilateral tariffs without congressional approval.

• Call off the lap dogs. Speaker Paul Ryan could back up his verbal support for the Mueller probe by signaling to his colleagues that they should stop their attempts to obstruct and undermine the investigation. Better yet, he could force the embarrassing Devin Nunes, Republican of California, out of the chairmanship of the House Intelligence Committee.

In addition, Congress could draw on the model of the post-Watergate era and adopt bipartisan legislation limiting the abuse of presidential power and strengthening public integrity and anti-corruption legislation. This would include requiring the release of the tax returns of presidential candidates, the extension of conflict-of-interest laws to the president and members of his immediate family, requiring the divestment of ongoing business investments and a ban on the acceptance of foreign emoluments.

Perhaps most important, Congress could reaffirm that no one, including the president, is above the law.

None of this requires that anyone abandon his or her conservative principles or legislative agenda. But it would go a long way to demonstrating that Republicans have not lost their souls as well as their spines.