Third, and perhaps most importantly, Trump knew full well how ill-advised an abrupt withdrawal from Syria would be because he tried to do it once before, in December 2018. In response, Secretary of Defense James Mattis resigned in protest and a broad coalition in Congress voiced its strong opposition to the withdrawal.

Peter Beinart: Democrats are hypocrites for condemning Trump over Syria

Less than a year later, all it took to convince Trump once again that Mattis and nearly every serious foreign-policy and security leader from either party in Congress were wrong was a phone call with Erdoğan, the increasingly authoritarian leader of Turkey.

The president apparently chose to listen to the Turkish dictator instead of his top advisers and the bipartisan consensus in Congress because he thought it would make a good campaign talking point.

While we need to do everything we can to limit the impacts of the president’s decision, members of Congress also need to ask ourselves what we can do to prevent Trump from letting other dictators steer U.S. foreign policy as Erdoğan has done.

What’s to stop Trump from pulling the United States out of the North Atlantic Treaty Organization, offering up Taiwan to China’s President Xi, or handing over Estonia to Vladimir Putin? What about withdrawing our troops from South Korea to secure a nuclear deal with Kim Jong Un or abandoning the Baltics to secure peace in Ukraine? Those terrible ideas might strike Trump as bold strokes designed to bring our troops home, too.

We can’t let any of those hypothetical situations come to fruition, because, as we have seen in Syria, the vacuum of American leadership is quickly filled by adversaries.

If the Senate fails to act now to constrain the president and dissuade foreign dictators from asking Trump to desert longtime allies, disregard U.S. interests, and overturn years of U.S. foreign policy, we will have no one to blame but ourselves. It’s true that foreign policy is primarily driven by the executive branch, but it’s Congress’s role to establish guardrails, particularly when the president cannot be trusted to pursue American interests.

Read: The intelligence fallout from Trump’s withdrawal in Syria

The Senate needs to put Trump, our national-security leadership, our allies, and the strongmen with whom Trump regularly flirts on notice. We need to demonstrate to dictators that our system is different: Congress can constrain the president and punish dictators for acting against our interests. There is broad bipartisan support for doing so in this case, and that should extend to preventing a repeat performance.

The Senate must preemptively put in place mechanisms to defend our democracy and our network of alliances before Trump acts against our interests once again, whether to indulge his isolationist impulses or to distract from impeachment.