The sun shines on the U.S. House of Representatives early in the morning. (Win McNamee/Getty Images)

This week, the House of Representatives did something increasingly rare: It overwhelmingly agreed on a major issue — in this case, stating that the Islamic State is committing genocide.

In doing so, the House, including almost all Democrats, potentially put itself at odds with the president. That's because the Obama administration is still deciding whether to use the g-word with regard to the Islamic State.

That the House got ahead of Obama doesn't surprise Cornell Law professor Jens David Ohlin, who says Monday's vote was yet another example of Congress trying to exert its influence over the president on foreign affairs. And those battles are much more common than bipartisan agreements.

"There's a constant tug of war between Congress and the president over who gets to speak for the U.S. government," he said. "It's an unresolved tension that goes back to the foujnding of our nation."

On Monday evening, the House voted 393-0 to condemn as genocide the Islamic State's violence toward religious and ethnic minorities in the region. The events leading up that vote appeared to be fairly bipartisan as well. Roughly 30 percent of the resolution's 218 co-sponsors are Democrats. And before a House committee unanimously approved the resolution, members of both sides expressed frustration the administration had not yet acted to make its own genocide designation.

The bipartisan nature of this resolution speaks to the degree to which lawmakers feel the terrorist group needs to be publicly censured — and to the degree with which they hope the administration follows their lead.

The Associated Press reports Secretary of State John F. Kerry could decide whether to apply the label to the Islamic State this week. If the Obama administration does side with the House, it would make history as only the second time the United States has put such a label on a conflict as it's happening — not afterward. The first was in 2004 in Sudan's Darfur region. (By contrast, Congress has now voted three times to designate ongoing events as genocide.)

Congress's resolution can't force Obama to do anything one way or the other, and it's unclear if the Senate will even take it up. The administration is possibly biding its time with a decision with regard to the Islamic State because a genocide designation could carry with it moral, political and even legal implications to step up U.S. military involvement in Iraq and Syria to stop the genocide.

House Speaker Paul D. Ryan (R-Wis.) criticized the perceived hesitation. "As the administration waffles on this issue and doubles-down on its failed strategy to defeat [the Islamic State], the American people are speaking loudly and clearly on this issue," he said in a statement.

It's a notable episode in the tug-of-war over foreign affairs that has been going on between the two branches for decades — even centuries. And it's something we're starting to see more of as Obama turns to foreign affairs in the twilight of his presidency.

Over the past year or two, this tension between Congress and Obama has manifested itself in Guantanamo Bay, the peace process in the Middle East and what actions to take against the Islamic State, among other issues, Ohlin noted.

Take the prison in Guantanamo Bay, Cuba, for example. Obama's signature 2008 campaign promise was to close it, and he recently released a plan to do so. But Republicans in Congress don't want it closed. And they've built up enough political opposition — even threatening to sue if he goes around them — that the prison will most likely stay open when Obama leaves office, albeit the number of prisoners drastically whittled down. And many Democrats have reservations about this, too, joining with Republicans to block funding for the closure of the prison.

Another foreign policy flashpoint between the two branches was so controversial that it looped in a third branch of government. In June, the Supreme Court decided Congress had overstepped its constitutional bounds by passing a law allowing Americans born in Jerusalem to list "Israel" as their birthplace on their passports. (For the past 60 years, the U.S. has also said it doesn't recognize Jerusalem as belonging to Israel.) Only the president gets to recognize sovereign foreign nations, the court said.

There are also foreign policy issues where Congress has actually relinquished some of its power, sometimes to the dismay of the president. For example, Obama has repeatedly asked Congress to authorize his use of military force to fight the Islamic State. Even though Ryan has endorsed the idea of debating  it, it's unlikely Congress will act. And Obama will probably continue launching airstrikes without a formal declaration of force from Congress like some argue the Constitution requires. The reason? Some members would quite simply rather not vote to authorize another war that might end up being unpopular.

That the House did come to an agreement on designating the Islamic State's violence as genocide suggests two things: It's politically much more popular than approving military action. And when it comes to Congress's power, sometimes exerting it is more important than partisanship.

Correction: This story misstated Ryan's views on whether to authorize the use of military force against the Islamic State. He supports having a debate on it but does not support it. Ryan believes the it will tie the president's hands.