President Donald Trump has gone to great lengths to break from the policies and approaches of his predecessor. Yet, when it came to justifying a round of U.S. military missile strikes in Syria, the new commander in chief dusted off a legal rationale crafted by Barack Obama’s administration.

Like the 44th president, Trump contended that the Constitution vests in the office of the presidency enough war powers to carry out some isolated military operations without lawmakers’ approval.

And as Congress returns this week to tackle two hot-button issues, a government funding bill to avert a shutdown and perhaps another try at a health care overhaul, it appears doubtful they will demand a new force-authorization measure from the Trump administration.

Experts who have studied war powers for years are quick to note that a widely agreed-upon definition has never emerged among legal and national security scholars about just where the office of the president’s authorities end. Court decisions and precedent have long tended to side with the executive branch, while the U.S. Supreme Court has stayed mostly mum, allowing pro-executive lower court decisions to stand.

“Constitutional practice over 228 years has seen a slow and steady expansion of unilateral presidential war powers,” Harvard Law School professor Jack Goldsmith wrote recently. The office of the president’s power has grown “mostly” with the “support or at least seeming-acquiescence of Congress,” he said.

In 2013, when President Barack Obama decided to seek congressional authorization for a Syria strike he ultimately never ordered, he said, “I have the authority to carry out this military action without specific congressional authorization.”

Kathryn Ruemmler, then-White House counsel, reportedly explained that the office of the presidency possessed authority to act on its own due to “important national interests” of stabilizing the region and enforcing international norms on chemical weapons use.

Trump’s legal counsel appears to have studied the Obama team closely. In his remarks on the night of the strike, Trump used language his top aides have echoed since: “It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons.”

He also sounded like Obama when he cited enforcing international norms as a legal rationale: “There can be no dispute that Syria used banned chemical weapons, violated its obligations under the Chemical Weapons Convention and ignored the urging of the U.N. Security Council.”

Goldsmith noted after the strike that he could “imagine the smile on Trump administration officials’ faces when they figured out that they would both enforce a red line that Obama wouldn’t and rely on Obama administration legal thinking to provide cover for doing so.”

Syria aftermath

The day after the U.S. missile strike on Syria, members of Congress emerged from a closed-door, classified briefing about the Trump administration’s actions with little to report about a long-term White House military plan.

That seemed just fine to most lawmakers who attended, few of whom seemed inclined to flex any congressional war powers muscle.

Sen. Jeff Flake was among that group. The Arizona Republican, a member of the Foreign Relations Committee, said Trump likely had legal cover for a one-off attack. But Flake also offered a perspective that reflects a long pattern of lawmakers on both sides of the aisle yielding more and more of their constitutionally granted war powers to the executive branch — no matter who occupies the Oval Office.

“Obviously, they’re not going to tell us what the long-term plan is, or the next step is,” Flake told a group of reporters after the briefing. “That wouldn’t be proper.”

The U.S. Constitution and some of Flake’s colleagues, however, suggest otherwise.

Article I, Section 8, Clause 11 of the U.S. Constitution clearly grants Congress the exclusive authority to declare war. Hammering a sovereign country with high-tech cruise missiles meets just about any scholarly definition of an act of war.

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“The president has already, in 75 days, conducted the first ground operations in Yemen, the first ground operations in Syria, and now air attacks in Syria,” said Virginia Democratic Sen. Tim Kaine, his party’s 2016 vice presidential nominee and the chamber’s leading advocate for a new force-authorization measure. “So we ought to be worried about it.

“And at the beginning of the administration, it’s time to get it right or it’s going to race away from us and we’ll regret it,” Kaine said on April 7.

Whether there would be much regret is debatable, even if Trump sends in American ground forces.

The last legislative days before the Easter recess were busy: Majority Leader Mitch McConnell changed the Senate rules to nix the filibuster for Supreme Court nominations, and the chamber voted to confirm Neil Gorsuch as a high court justice; Trump greenlighted launching nearly five dozen Tomahawk missiles at a Syrian air base, and lawmakers wanted some answers on the strike before they left.

Chaos filled the hours before the Senate left for recess on the day after the strike.

There was no time for White House officials and senators to craft a new authorization for the use of military force, or AUMF, measure for the Syria operation — and perhaps future ones — and rush it to the Senate floor. The House was long gone, having departed the previous day, by the time the first Tomahawk was launched. Even without the time crunch, consensus building around such an authorization would likely have taken months.

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On their way out, senators seemed mixed about the need for a new AUMF tailored specifically for the April 6 attack and possible future Syria strikes. They also appeared split on whether Congress is further giving away its collective constitutional war powers.

Some key Republican members who have been involved in the AUMF debate for years say Article II of the Constitution and years of Supreme Court and other federal judicial decisions give the White House all the legal cover it needed for what lawmakers expect was a one-time strike.

“I think they have a legal basis to do what they did,” Senate Foreign Relations Chairman Bob Corker said. “But I think before you start looking at an additional authorization, I think you need to know what they [might] attempt to do. This was a short operation, 59 Tomahawk missiles.”

“There’s no point in an AUMF today. He acted under authorities he has as commander in chief under Article II,” the Tennessee Republican said. “If there’s going to be additional activities, then we would need to do that.”

Any force-authorizing measure would have to move through Corker’s committee, meaning he would wield a key pen in the crafting of whatever the Senate might pass.

What’s next?

Yet, within the Republican Party there are differences on the question of whether Congress hands away more and more war power when it opts against authorizing U.S. military combat operations.

“It depends on what happens next,” Flake said. “If there is a plan to go forward with safe zones or no-fly [zones] — and that was not discussed at all — certainly there would be a need for an authorization.” The Arizona lawmaker said the April 6 strike, however, did not require congressional approval.

[Don’t Expect Military Force Authorization for Syria Soon]

Over in the House, some lawmakers who support Trump on other matters believe Congress would be handing over power if it does not return this week and move to craft a new authorization.

“President Trump has declared a more aggressive approach to fighting terrorism, and his actions give every indication that — unlike President Obama — when this President draws a line in the sand, crossing it will have consequences,” said Oklahoma Rep. Tom Cole, a House GOP deputy whip.

Cole describes himself as a “firm believer” that commanders in chief deserve “maximum flexibility when … waging war.” But he also believes “that the Congress has a role in committing our troops to battle,” he said.

“Going forward, President Trump needs to seek an AUMF from this Congress before taking further military action,” Cole said.

Christine Wormuth, Pentagon policy chief under Obama, said lawmakers should craft a new authorization measure that is tailored for the changes in how the U.S. fights against extremist groups in the Middle East since 2001, when lawmakers hurriedly passed a broad measure after the 9/11 attacks.

“My sense is it would be helpful if there was a new one for the Middle East as it exists today, and for the fight against ISIS and similar groups,” she said. “And it would put the country on a firmer footing legally, while preserving the balance of power between the branches of government.”

Yet, Wormuth said she is “not at all sanguine that this administration is going to get one.”

The 2013 effort to craft an updated AUMF died when lawmakers failed to agree on scope and definitions of what U.S. forces would be allowed to do on the ground. Wormuth concludes that little has changed on the Hill since.

“It sure sounds like the same disagreements are still there in Congress,” she said. “You have two broad schools of thought: One school wants a broad authorization to prosecute the war on terror, and a second school that wants an authorization circumscribed to what they feel comfortable with. Squaring that circle isn’t easy — and isn’t likely to happen.”