President Trump and Russian President Vladimir Putin shake hands at the beginning of a meeting at the Presidential Palace in Helsinki. (AP)

Modern presidents drive U.S. foreign affairs. Congress struggles to compete with the energy and unity of the executive that were heralded by Hamilton.

But President Trump’s performance this week — including his asking “what good is NATO?” in Brussels, his criticism of Prime Minister Theresa May in Britain and his embrace of Russian President Vladimir Putin in Helsinki — has raised alarm on both sides of the aisle. Can Congress rein in a wayward president?

The answer is yes. Congress may no longer play the lead role envisioned in Article I of the Constitution. But it has the tools to influence the course and conduct of U.S. foreign policy. Though presidents play the lead role, in cases from Korea to Vietnam, from Central America to Somalia and Iraq, Congress has consistently frustrated presidents’ ambitions, even in wartime.

Congressional opponents of the president’s policies routinely rely on three main tools: criticizing the administration publicly; conducting investigative oversight hearings; and enacting legislation.

The current Congress has already used each of these to push back against Trump on Russia. But will it do more?

1. Members of Congress can speak out publicly

Here’s one of the most important, if indirect, ways in which Congress can influence foreign policy: battling the administration in the court of public opinion.

Heading to the cameras may seem like empty theatrics. But public criticism can help shape popular opinion. Turning the public against the president can pressure the administration to change course.

That may have begun. Until now, many of Trump’s actions and policies been criticized and condemned by Democrats — and occasionally by a handful of Republicans. But Trump’s Helsinki comments triggered outcry from across the political spectrum.

If sustained, public criticism from fellow Republicans could mean serious trouble for Trump. Trump’s approval ratings are already historically low, particularly for a president enjoying a robust economy. Only overwhelming support from his partisan base prevents Trump from falling to the levels President Richard Nixon saw by the end of the Watergate hearings — and Republican criticism could erode that support.

The wide and intense backlash from congressional Republicans and conservative media outlets has already forced Trump to walk back his Helsinki statement, to declare his faith in U.S. intelligence agencies and to declare that he would not allow the Kremlin to question a former U.S. diplomat. If Republican criticism continues, it could change Trump’s political calculus as he deals with Putin.

2. Congress can hold hearings

Oversight hearings may appear to be a weak tool against the commander in chief. But they can be highly influential for two reasons. First, the presidency’s most important institutional advantage in foreign affairs may be its superior access to information. Vigorous oversight helps Congress close this gap.

Second, investigative oversight gives congressional critics a bully pulpit from which to battle the White House in the public sphere. By aggressively questioning administration officials and shining a light on perceived missteps or abuses, congressional critics can raise the White House’s political costs for going its own way.

Historically, Congress has wielded this power to great effect. For instance, congressional investigations into Harry Truman’s conduct of the Korean War seriously hobbled the administration and encouraged Truman not to seek reelection in 1952. From 1966 to 1971, Sen. William J. Fulbright held extensive hearings questioning the conduct of the war in Vietnam, which became a significant political headache for President Lyndon B. Johnson and Nixon. And congressional oversight of President Ronald Reagan’s policies in Central America brought to light the administration’s clandestine (and illegal) operation to fund anti-Communist rebels in Nicaragua by selling arms through Israel to Iran. The Iran-contra scandal, as it was called, shook the administration to its core.

Similar investigatory hearings have plagued the last three administrations, into the “Black Hawk down” incident in Somalia under President Bill Clinton; into prisoner abuse at Abu Ghraib under President George W. Bush; and into the fatal attack on the U.S. Consulate in Benghazi, Libya, under President Barack Obama. Through these, congressional committees influenced U.S. foreign policy significantly.

Congress’s current Russia probes have already produced three important results.

First, committee hearings — particularly the public testimony of former FBI director James B. Comey after Trump dismissed him — helped build political pressure that forced Deputy Attorney General Rod J. Rosenstein to name a special counsel to investigate possible Russian interference into the 2016 elections.

Second, the revelations from these investigations helped pressure congressional Republicans to enact Russian sanctions legislation, despite White House opposition.

Finally, the Senate Intelligence Committee’s initial and bipartisan report affirming U.S. intelligence agencies’ conclusions that Russia did interfere to aid Trump made it still more explosive when, in Helsinki, the president appeared to accept of Putin’s denial of such interference.

3. Congress can pass legislation

Congress’s most obvious tool is the power to enact legislation. It’s also the most difficult to use, especially when the same party controls both Congress and the White House. Republicans on Capitol Hill have strong incentives to avoid or block legislative efforts that counter a Republican president. And, of course, any bill risks Trump’s veto.

But when investigations and public criticism have eroded the president’s support, they have also often prompted new law.

Congress has already rebuked the president this way, twice, on Russia: in 2017, by passing a law imposing new sanctions on Russia for its electoral meddling; and yesterday, with its nonbinding resolution on protecting U.S. government officials, past and present. And when the Trump administration initially refused to implement the sanctions law, congressional criticism — including from many Republicans — helped change the administration’s position.

So what’s next?

But will congressional Republicans truly and permanently break with the White House over Russia? After all, Republican resistance to Trump’s tariffs quickly sputtered. However, this time it could be different.

For 70 years, a strong stance against Russia has been a core commitment of the party of Reagan. Equally important, while Trump’s populist positions on trade (which also violate party orthodoxy) resonate with his base, there is scant public support for Trump’s embrace of Putin and the Kremlin.

Historically, members of Congress challenge a president of their own party when they believe the benefits of distancing themselves from the White House exceed the costs of weakening their party leader. That happened, for instance, in 1968, with a rising Democratic tide against Johnson’s war in Vietnam.

We will find out whether, for Republicans, the benefits of defending the Reagan legacy exceed the costs of crossing a president whose relationship with Russia is out of step with public opinion.

Douglas L. Kriner is a professor of political science at Cornell University.