President Obama’s speech Wednesday night, announcing expanded strikes against the Islamic State terrorist group, had its fair share of confusing parts. There were the shoehorned references to fighting Ebola and the auto industry. There was his favorable citations of Yemen and Somalia as examples of this new, expanded bombing campaign, even though, as The Post’s editorial board wrote, “Somalia is a failed state and Yemen is hardly a healthy one; both remain incubators of dangerous terrorism.” There was no clear description of what “destroying” the Islamic State would look like, let alone a time frame to achieve that goal. And there was the inexplicably large chunk of “rah rah America” that took up much of the end, and, as far as anyone can tell, served little point other than to fill time. (“I was going to oppose bombing those terrorists, but then he reminded me how awesome America is,” said no one ever.)

But the most inexplicable part of the speech was Obama’s refusal to ask Congress to authorize the new campaign. There is simply no reason for the president to go it alone on this campaign, with only Congress’s “consultation.”

Politically speaking, it’s well known that Congress doesn’t want to be called to account on bombing the Islamic State. As one congressman told the New York Times:

“A lot of people would like to stay on the sideline and say, ‘Just bomb the place and tell us about it later,’ ” said Representative Jack Kingston, Republican of Georgia, who supports having an authorization vote. “It’s an election year. A lot of Democrats don’t know how it would play in their party, and Republicans don’t want to change anything. We like the path we’re on now. We can denounce it if it goes bad, and praise it if it goes well and ask what took him so long.”

For Democrats, the fact that the party is split is no reason not to have a vote on the issue, since senior Republicans say the president in the end would have enough votes from both sides to pass an authorization. More importantly, holding a vote would force congressional Republicans to attach themselves to Obama’s new war, undermining their craven plan to, as Kingston said, “denounce [Obama’s plan] if it goes bad, and praise it if it goes well.” And don’t voters deserve to know where their representatives stand on bombing the Middle East yet again before deciding whether to reelect them?

Calling for Congress to authorize the expanded operations would also allow Obama to return to a position he held before voters placed him in the White House. As Buzzfeed’s Gregory Johnsen pointed out Wednesday, Obama said while campaigning for president, “The president does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation.” This is absolutely correct, despite the efforts of presidents from Lyndon Johnson onward to expand the executive branch’s warmaking powers (and Congress’s continual willingness to duck tough votes). Obviously, Obama has already reversed his stance on this to authorize drone strikes in Somalia, Yemen and elsewhere. But a year ago, he requested congressional authorization to bomb the Assad regime in Syria. Given that he’d almost certainly get Congress’s backing, there seems to be little reason to ditch his rediscovered respect for checks and balances.

Finally, the decision not to seek that approval leaves Obama’s new war on extremely shaky legal ground. White House officials are claiming that the campaign is legally justified by the 2001 Authorization of the Use of Military Force, passed in the wake of the Sept. 11 attacks. There’s one small problem: That authorization allows the president to attack al-Qaeda and its harborers, and the Islamic State is definitely neither of those things. Al-Qaeda has specifically denounced the Islamic State, and even liberal experts have called any linking of the two groups “laughable.” One would think a former constitutional law professor would be ashamed to resort to such questionable legal authority, and again, the easiest way to solve the issue is to simply ask Congress for a vote.

Sadly, Obama’s bypassing of Congress looks to be another case of a president enamored with expanding his own powers. But it is a farcical decision, and the sooner he fixes it, the better for him, for Congress, and for the country.