For six years, Republicans railed about President Obama’s “usurpation” of power. So it’s no small irony that, in one of their first acts since taking control of Congress, they are planning to invite him to usurp some more.

On Tuesday morning, a group of tea party conservatives met in the Capitol complex to complain about Republican plans to pass “trade promotion authority,” giving Obama greater ability to negotiate trade deals with less congressional say-so.

“At a time when the president has, for all intents and purposes, declared war on the Constitution’s separation of powers, it makes absolutely no sense for Congress to voluntarily give away its treaty ratification prerogatives,” complained Rick Manning, president of Americans for Limited Government.

Niger Innis, executive director of TheTeaParty.net, said Obama “has shown outright contempt for the separation of powers,” and “there can be no worse lesson for the White House than for this Congress to voluntarily cede authority to it.”

After that session, I took a short walk to the Heritage Foundation, where Sen. Rand Paul, R-Ky., a leading defender of congressional prerogatives, was giving a speech in which he offered his view that “the president has usurped and created a broad executive-branch power that is not there.”

So I asked Paul about trade promotion authority, in which Congress surrenders its ability to amend trade deals negotiated by the president. Paul said conservatives’ objections are “valid,” but “I’m also a big believer in free trade, and I think free trade is a good thing.” He noted that “the good of trade has caused me to vote for things that I think aren’t perfect.”

In other words, Obama is usurping power – unless Rand Paul agrees with the policy outcome.

The internal Republican struggle over trade is part of a larger tension: Even as Republicans lay the cornerstone of their new majority, there are already cracks in the foundation. This is an inevitable byproduct of taking unified control of the legislature. Now it’s no longer enough to stop Obama, and Republicans must come up with their own agenda.

The latest instance of the party’s right hand not knowing what its far-right hand is doing comes from National Journal’s Daniel Newhauser, who reported Tuesday that a rump group of conservative purists is about to bolt the House Republican Study Committee – until now the main caucus for conservatives – because it hasn’t been combative enough with Republican leaders.

There’s also a split over military matters. At Heritage’s conservative policy conference Tuesday, for example, Rep. Jim Bridenstine, R-Okla., a Navy pilot, called for billions of dollars to be sent to Ukraine and proposed that the United States provide Ukraine with “lethal military aid” to fight Russia.

He proposed that Republicans send an “unmistakable message to Obama … a man clearly uncomfortable with accepting America’s natural and manifest role as a global superpower.”

But preceding Bridenstine on stage was Paul, who told the same audience that the United States needn’t “be involved in every war and every skirmish” and criticized U.S. interventions in Libya and Iraq.

The foreign policy split will recur for Republicans, but trade will likely split them first. Backed by labor unions, many, if not most, Democrats will oppose trade-promotion authority, which will require a large number of Republicans to back the legislation. Yet roughly 30 House Republicans are already on record opposing the trade legislation, and Curtis Ellis, an organizer of Tuesday’s anti-trade meeting, predicted a “significant minority” would end up in opposition.

That’s particularly so if the uglier sentiments expressed at Tuesday’s anti-trade gathering gain traction. Conservative Frank Gaffney alleged that the perpetrators of last week’s massacre in Paris had the same agenda as the Obama administration: to “impose Sharia law worldwide, including in this country.” The American Family Association’s Sandy Rios agreed that Obama would use trade pacts “to bolster the practitioners of Sharia (and) some Republicans want to help the president do so.”

Standing against such rot would be noble, but it would require Republican lawmakers who howl about Obama the usurper to concede that strong presidential power can be a good thing.

Dana Milbank is a columnist for The Washington Post. He can be contacted at:

danamilbank@washpost.com