Washington • If there’s one thing Sen. Mike Lee is known for, it’s his staunch defense of congressional powers.

After all, Lee points out, the U.S. Constitution starts with Congress in Article I — and the presidency is Article II.

His protection of the legislative branch helps explain how the usually congenial Utah Republican erupted after a closed-door briefing by military leaders and Trump administration officials over its strategy toward Iran, calling their answers “insulting,” “demeaning,” and ultimately “un-American.”

Why is Lee standing up to Trump?

Lee explained to reporters at the Capitol and later on NPR that the briefers attempting to defend the administration’s actions against Iran — including the killing of Iran Maj. Gen. Qassem Soleimani — treated members of Congress essentially with kid gloves, refusing to answer specific questions about what point the White House would seek approval for military action.

The Utah senator's comments went viral and earned him plaudits from some on the left and right for standing up to the White House.

Lee says the briefers left after 75 minutes “while they’re in the process of telling us that we need to be good little boys and girls and run along and not debate this in public.”

That doesn’t sit well with Lee who enjoys citing the Federalist Papers, letters written by Founding Fathers to prop up passage of the Constitution, and how they specifically enshrine powers of war to Congress, not the presidency.

“Senator Lee is very attentive to the meaning of words, especially in the Constitution and statutes generally, and to checks and balances and separation of powers specifically,” says Carl Tobias, a law professor at the University of Richmond.

Does Lee have a point?

While the president has the authority to take short-term military action, it's up to Congress to approve any long-lasting conflict. At least that's how it's supposed to work.

In actuality, Congress hasn’t declared war since World War II and has continued to give the president power to march U.S. forces into battle over and over again. After the terrorist attacks of Sept. 11, 2001, Congress essentially gave carte blanche to the president to take what action he deemed necessary.

Lee had said he was initially unsure whether he would back a measure pushed by Sen. Tim Kaine, D-Va., that would force a debate and vote in Congress to escalate any further escalation with Iran. But after the briefing, Lee says he was on board as long as there are a few tweaks.

The House passed that measure Thursday, though it’s unlikely to muster the 60 votes it needs in the Senate to get through.

However, Lee isn’t alone in raising concerns about never-ending wars. Trump had complained about them himself in withdrawing American troops from northern Syria. And Lee has gone out of his way to say his frustration is not directed at the president, but at the president’s advisers.

Is Lee going this alone?

Sen. Rand Paul, R-Ky., stood side-by-side with Lee as the Utah senator railed about the Iran briefing and backed him up on key points.

Other Republicans, though, aren't backing them up.

“I have said for decades that I believe the War Powers Resolution is unconstitutional,” Sen. Lindsey Graham of South Carolina tweeted. “If you don’t like what the Commander in Chief is doing — cut off funding.”