House Speaker Paul D. Ryan (Wis.) has joined his fellow Republicans in coming out strongly against President Trump's proposed steel and aluminum tariffs. “We are extremely worried about the consequences of a trade war and are urging the White House to not advance with this plan,” Ryan spokeswoman AshLee Strong said Monday. The comment came shortly after the speaker's office highlighted a news article about how fears of a trade war had already hurt the stock market.

The good news for Ryan and these Republicans: There is something they can do about it! They could, you know, actually pass a law.

The Constitution explicitly grants Congress power “To regulate Commerce with foreign Nations” — a power that necessarily includes the ability to impose tariffs. The only reason Trump can impose the 25 percent steel tariff and 10 percent aluminum tariff is that Congress has granted him some tariff authority. “While the Constitution gives the President authority to negotiate international agreements,” a 2016 Congressional Research Service report states, “it assigns him no specific power over international commerce and trade.”

The White House will probably justify the new tariffs under a law Congress passed in 1962 called the Trade Expansion Act. This allows the president to take action to “adjust the imports” of certain items if the Commerce secretary “finds that an article is being imported into the United States in such quantities or under such circumstances as to threaten to impair the national security.”

This particular protection has not been used by a president in more than 30 years, which has led to plenty of griping about whether the tariffs would be legal. Is excessive importation of steel and aluminum a genuine national security threat? And if so, why has Trump floated the possibility of Canada and Mexico being exempted?

But even if the tariffs are legal, Congress could move to block them. The many Republicans decrying the change, including Ryan, haven't specified whether they might back a push to do so. (So far, it's just whispers.) But both Ryan and the GOP leader of the Senate, Mitch McConnell (Ky.), strongly oppose them and could lead the charge.

There is some precedent for the GOP-controlled Congress doing something over Trump's objections. It did so when it almost unanimously passed new sanctions against Russia that Trump wound up signing against his will. In that case, of course, Congress had way more than enough votes to override his veto; in this case, Republicans would need substantial support from Democrats to get the two-thirds majorities they would need (assuming Trump would employ his veto pen). Democrats and labor unions have been much more supportive of the tariffs, but even with more protectionist views of trade, you have to believe that plenty of them would be tempted to join in a GOP-led rebuke of Trump.

Alternatively, the GOP leaders could try to halt the tariffs by inserting something into a must-sign piece of legislation, such as the government-funding bill that is due later this month.

Republicans will be reluctant to go down this path, less for practical reasons than for political ones. When it comes to running afoul of Trump, they have been burned over and over again, and it has led all of them to pick their battles very carefully. They would have to feel very strongly about this particular battle to risk a chasm within the party.

But on a basic level, not doing anything except complaining would be ignoring their own constitutional mandate.