Try as they might, there is little that members of Congress can do to keep President Trump from taking the country to war if he really wants to.

They are trying. The Senate on Wednesday gave initial approval to a resolution that limits the president's authority to launch attacks on Iran — just a few weeks after Trump brought the country to the brink of war by ordering the assassination of Iranian Maj. Gen. Qassem Soleimani. Amazingly, the resolution even had bipartisan backing: Eight Republicans joined the Democrats to pass the measure.

"While the president does and must always have the ability to defend the United States from imminent attack, the executive power to initiate war stops there," Sen. Tim Kaine (D-Va.) said before the vote. "An offensive war requires a congressional debate and vote. This should not be a controversial proposition. It's clearly stated in the Constitution."

The president, of course, seems to consider the Constitution an annoyance — he bristles at any check on his power. On Wednesday, he argued against the resolution via Twitter:

The resolution is bound to fail: Trump will almost certainly veto it when it comes to his desk. But even if Congress passed the bill with a veto-proof majority, it might do little to constrain Trump — or any other president determined to go to war with Iran.

Presidents, after all, tend to take a very expansive view of their Constitutional commander-in-chief duties — and Congress, this new resolution notwithstanding, has often proven feckless about asserting its own prerogatives in warmaking. In 2006, Democrats won control of both the House and the Senate after Americans became tired of the war in Iraq — but they not only failed to end the war, then-President George W. Bush doubled down with a "surge" of troops to that country, deepening and lengthening U.S. involvement in combat there. Similar examples abound in U.S. history.

The Iraq War, of course, had authorization from Congress. The new resolution would ostensibly require Trump to seek similar backing. But Kaine's own comments hint at an opening that would let the president disregard that requirement: All Trump has to do to send U.S. forces into combat is say that he was aiming to prevent an "imminent attack" from Iran.

In fact, that was one of the many rationales that White House officials offered for the Soleimani assassination in January — Trump even at one point suggested Soleimani was plotting to strike as many as four U.S. embassies. Trump probably made up those plots, but it didn't matter. He ordered the strike on Soleimani without informing congressional leaders, and by the time the dust had cleared, Soleimani was dead and the U.S. at the precipice of a wider war with Iran — until cooler heads prevailed.

The incident was one more reminder that you should never believe a word this president says. And Americans have learned they should expect him to bypass the restraints that previous presidents observed. So it isn't difficult to imagine a scenario in which Trump sent American forces into action without congressional approval — claiming an imminent attack, but offering no proof — then dared the House and Senate to do something about it. As already noted, history doesn't suggest Congress would rise to that challenge.

In such a scenario, it is possible that the House could use its power of the purse to defund American military operations against Iran and thus force the president to bring the troops home. Politically it would be difficult — Trump could accuse lawmakers of failing to support American soldiers already in combat. And it's unclear whether the president would bend to such tactics.

After all, Trump has already bypassed Congress on a funding matter once, using the defense budget to begin construction of a wall on the border with Mexico — after Congress refused to provide that funding in the first place. That dispute is still in the courts, but it offers an ominous guide to the president's willingness to bypass normal constraints.

Hopefully, these scenarios don't come to fruition. Trump is somewhat famously unpredictable on the matter of war with Iran. He came to office promising to end Middle Eastern wars, and once called off an attack on that country's forces. But he also ordered Soleimani's assassination, and his policies toward Iran seem likely to keep tension high between the two countries. It is a good thing that the Senate is trying to act on a curb against his more aggressive tendencies. If the president wants war with Iran, though, it will be tough to stop him from getting it.

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