WASHINGTON -- U.S. Congress is moving toward doing something it hasn't done since the Vietnam War -- repealing authorizations for the president's use of military force. For lawmakers, that's an important gesture toward reclaiming a say over the wars America wages abroad.

The Senate voted 66-30 on Wednesday to repeal the 2002 resolution giving President George W. Bush the green light to invade Iraq, an authorization that many now see as a mistake. The measure also would repeal the 1991 resolution authorizing the U.S. military's combat action against Iraqi leader Saddam Hussein's invasion of Kuwait.

Approval by the House, which is less certain, would officially end congressional approval for the U.S. war in Iraq and, symbolically at least, close the U.S.-led war itself.

Debate on repealing the 2002 authorization comes nearly 20 years after Bush stood in front of a "Mission Accomplished" banner to declare that U.S. troops had wrapped up major combat in Iraq. After that breezy moment of American confidence, the U.S. war went on to take the lives of hundreds of thousands of Iraqis and thousands of Americans.

The U.S. overthrow of Saddam and Iraqi security forces in 2003 opened the door for the rise of both Islamic State fighters and Iranian-allied political parties and militias in Iraq, as well as horrific sectarian violence. Only in December 2021 was the U.S. military finally able to declare an actual end to its combat role -- though 2,500 U.S. troops remain in supporting roles.

As the Iraq War's timeline shows, little about how the U.S. starts and ends its modern wars, and who gets to decide, is at all clear cut.

Here's a look at congressional action all this matters.

WHAT ARE THE AUTHORIZATIONS? WHY NEEDED?

First of all, an "authorization for use of military force" is not a declaration of war. Framers of the Constitution split responsibility over wars abroad between Congress and the president. They gave lawmakers authority on declaring and funding but the president -- as commander in chief -- authority to direct the waging.

That's what's in print, anyway. In practice, lawmakers since the Vietnam era have accused the executive branch of starting and pursuing foreign wars and launching military strikes without congressional sign-off.

In fact, the last war Congress formally declared was World War II, after the Japanese attack on Pearl Harbor.

An authorization for use of military force is kind of a war declaration-light, without the more drastic domestic actions that come with formally declaring the nation at war.

Presidents since the end of World War II have invoked the authorizations or claimed other legal justifications for the Korean War, Vietnam War, Operation Desert Storm, the wars in Afghanization and Iraq and dozens of more limited military strikes abroad -- without full-on declarations of war.

In Vietnam, President Lyndon Johnson used a 1964 congressional resolution for military force, after an alleged attack on U.S. ships, to steadily draw U.S. forces deeper into the increasingly unpopular war. U.S. intelligence findings justifying the 1964 resolution were later questioned. In the 1970s, Congress repealed the authorization and sought unsuccessfully to assert more control over America's foreign wars.

Still, a half-century later, congressional authorization for military force is a powerful signal that lawmakers are on the same page as the president in the need to wage a war abroad. So revoking that authorization sends a powerful signal, too.

WHY SCRAP THE 2002 AUTHORIZATION AND WHY NOW?

War fatigue drained public support for both of the post-Sept. 11, 2001, wars, in Afghanistan and Iraq, as the conflicts dragged on for longer and with far darker and deadlier results than the Bush administration and Congress had anticipated. Republican backing, decisive in passing the 2002 authorization, ebbed. That' was especially so as an isolationist trend in the party grew under President Donald Trump.

Advocates for repeal won broad and bipartisan support in the Senate on Wednesday, as well as backing from the White House. They argue a repeal shows the world that Iraq's current, democratically elected government is no longer a U.S. enemy and that Iraq has stabilized.

"It sends a message about America. We are willing to turn swords into plowshares," Sen. Tim Kaine, a Virginia Democrat and a main sponsor, told reporters.

Keeping congressional authorization for military force on the books "invites presidential mischief," giving administrations legal cover to launch new military strikes abroad without first consulting Congress, Kaine argued.

WHAT'S THE CASE FOR KEEPING THE AUTHORIZATION?

Opponents argue repeal would signal weakness, particularly to U.S. rival Iran, and invite Tehran to exert its influence in the Middle East even further. They also say the 2002 authorization is needed to make sure future presidents can respond quickly to threats.

"I am opposed to Congress sunsetting any military force authorizations in the Middle East," Senate Republican leader Mitch McConnell said this week. "Our terrorist enemies aren't sunsetting their war against us."

A March 23 drone strike that killed a U.S. contractor in Syria added impetus to that argument. The U.S. blamed an Iranian-allied militia.

Supporters of the repeal counter that presidents can and do cite a range of other legal arguments for authorizing rapid action when a security threat suddenly looms abroad. They point particularly to a separate 2001 congressional authorization for military force against extremist groups that was passed in the immediate aftermath of al-Qaida attacks on the United States. Senators last week resoundingly rejected a bid by Republican Sen. Rand Paul of Kentucky to repeal the 2001 authorization.

THE IRAQ WAR AND CONGRESS

Lawmakers arguing for withdrawing the 20-year-old authorization for the war in Iraq say it would be a step toward righting the balance of power between Congress and the president when it comes to launching into conflicts abroad.

Critics of repeal say Congress willingly yielded too much of its war powers to presidents, especially on the so-called "Forever Wars" in Afghanistan and Iraq that followed the 2001 al-Qaida attacks. Afghanistan became the longest war in U.S. history.

Unlike in every previous major war, Congress has allowed administrations to go into debt to pay for the Afghanistan and Iraq wars rather than draw on taxes, said Linda Bilmes, a public finance and policy researcher at Harvard's Kennedy School of Government. She has charted the resulting trillions of dollars in interest payments facing the U.S. from those two, two-decade conflicts.

Money from the borrowing limited financial scrutiny of the wars in Congress. It also allowed lawmakers and successive administrations to avoid touching off politically fraught debates over the rising costs, Bilmes said.

"It was something which was not in the interest of the American public," Bilmes said. "But it was in the interest of elected officials across the board to have minimal oversight."

WHAT'S NEXT?

Repeal of the Iraq War authorizations goes next to the House. It's not clear how broad the support for the repeal is there, or how soon any action might come. House Speaker Kevin McCarthy has suggested he is open to supporting repeal, although he previously opposed it. President Joe Biden says he supports the repeal and will sign it if it gets to his desk.