President Trump has a big constitutional decision to make regarding the attack launched on Friday by United States, British and French forces against Syria for its use of chemical weapons. And he should make it this week.

When he launched his first retaliatory strike against Syria a year ago, the president almost immediately informed Congress, explaining that he was acting in a manner “consistent with the War Powers Resolution.” The resolution, passed over Richard Nixon’s veto in 1973, imposes strict limits on unilateral presidential war-making. It places the burden squarely on Trump to gain congressional approval of his decision to bomb Syria within 60 days; if he fails, he must cease his military campaign within the next 30.

Moreover, the resolution requires the president to notify both Houses “within 48 hours” of the initiation of hostilities, although presidents have taken liberties in meeting this deadline. It took Barack Obama 13 days before formally informing Congress after he announced his open-ended campaign against the Islamic State on Sept. 10, 2014. In contrast, President Trump’s letter arrived in the House and Senate within 48 hours of his initial bombing raid against Syria in April of 2017. It would be a bit much to insist that Trump should have already sent his new notification 48 hours after his speech on Friday night — since Congress was out of session over the weekend. But if Trump is to repeat his exemplary performance, his letter should arrive while Congress is in session this week and can prepare to consider its responsibilities under the resolution.

The first Syrian assault by the Trump administration was a one-shot affair, so the 60-30 timetable didn’t apply. This time around, Mr. Trump said that the United States is “prepared to sustain” the bombing “until the Syrian regime stops its use of prohibited chemical agents.” So if Mr. Trump follows his own precedent and promptly provides Congress with formal notice of his new campaign, he himself will be recognizing that the War Powers Resolution gives him 60 days to persuade Congress to approve his initiative.