The majority of US senators who voted Friday on an amendment to check and balance Donald Trump’s reckless approach to foreign affairs chose to send a clear and unequivocal signal about the desire of the Congress to restrict this erratic president’s ability to go to war with Iran. Unfortunately, an obstructionist block of Republican senators prevented the chamber from formally asserting its authority. These Republicans did so by casting votes that placed their loyalty to a president of their own party above the most basic premises of the US Constitution.

It is significant, arguably historic, that 50 senators voted Friday to amend the National Defense Authorization Act (NDAA) to prohibit federal funds from being used for military operations against Iran without explicit congressional authorization. (Additionally, a senator who missed the vote, Democrat Chris Coons of Delaware, had indicated that he would have supported the amendment.) Senate Democratic Leader Chuck Schumer (D-NY) was right to assert that “A bipartisan majority of the Senate today sent an important message to President Trump: You do not have a blank check to pursue another endless war in the Middle East.”

The problem is that 40 senators opposed the measure, and 10 more failed to vote on Friday. That meant that the proposal did not receive the 60 votes that were needed to amend the NDAA. This was a win for Senate majority leader Mitch McConnell, who griped that the amendment was an attempt to micromanage presidential decisions about war and peace. But McConnell and Trump apologists like Lindsey Graham (R-SC) know better. The Constitution explicitly states: “The Congress shall have Power… to declare War.”

Senator Tom Udall, the New Mexico Democrat who sponsored the amendment, made that point during the floor debate. “The president claims that he does not need congressional approval to launch strikes against Iran—but he is flat out wrong,” explained Udall, a key member of the Senate Foreign Relations Committee. “Article I, section 8 of the Constitution could not be clearer: it is Congress—and Congress alone—that has the authority to ‘declare war.’”

Senators who take seriously their oath to “support and defend the Constitution of the United States against all enemies, foreign and domestic” sided with Udall. “The Constitution is very clear that Congress has the authority to declare war and I am voting for this bipartisan amendment to prevent President Trump from starting an unauthorized war with Iran,” said Wisconsin Democrat Tammy Baldwin, who as a member of the House voted against authorizing the Bush-Cheney administration to attack Iraq. “I am always guided by the hard lessons that should be learned when America chooses to go to war in the Middle East. After 18 years of US military engagement in Middle East conflicts, Congress must not allow this administration to repeat the mistakes of the past. We have a constitutional responsibility to prevent the President from going to war and sending our American troops into harm’s way without congressional authorization.”

That sentiment was shared by a number of Republicans, including Kentucky Senator Rand Paul, who has repeatedly said with regard to Trump’s talking and tweeting about taking making unilateral moves that might lead to the “obliteration” of all or part of Iran: “The Constitution is very clear that we don’t go to war unless it’s voted on by Congress. The declaration of war is required to be voted on by Congress.” Paul was joined in voting for the resolution by several other Republicans, including Kansas Senator Jerry Moran, Maine Senator Susan Collins, and Utah Senator Mike Lee, who recently joined senators from both parties in sending the president a letter that declared, “Given that growing risk, we want to reiterate that, as of this date, Congress has not authorized war with Iran and no current statutory authority allows the US to conduct hostilities against the Government of Iran.”

The Udall amendment provoked a rare debate about the failure of the Congress to respect the role that is outlined for it in the Constitution. McConnell claimed that Udall amendment was an example of “Trump derangement syndrome” on the part of the Democrats. His claim was rendered ridiculous by the fact that Republican senators joined with their Democratic colleagues in voting to check and balance an administration that Schumer warned “may bumble us into (war).”

But McConnell kept playing the partisan card, claiming that “None of our Democratic friends would be supporting this if there was a Democratic president.” That was a lie. A number of Senate Democrats raised concerns during the presidencies of Barack Obama and Bill Clinton—as they did during the presidency of George W. Bush and as they have done during the presidency of Donald Trump—about the failure of successive Congresses to assert the authority of the legislative branch to constrain executives who are inclined toward military adventurism.

Those Democrats will continue to speak up in this tenuous moment, as will a growing number of Republicans. “We didn’t reach the 60-vote threshold we needed to pass it as an amendment to the defense bill, but the vote today demonstrates bipartisan concern that President Trump might pull our troops into an unnecessary war,” Senator Tim Kaine (D-VA) said Friday afternoon. “The debate doesn’t end here; The House now has an opportunity to pass this amendment.”

It should not end there, because those who speak up are not merely raising their voices against war with Iran. They are raising their voices for the United States Constitution.