The Iran war might be the end of Congress' war powers. What happened?

Congress will vote this week on whether to approve President Donald Trump's already in motion war on Iran, in what experts are calling a "tipping point" for the unique congressional power to declare war, eroded for decades by presidents they say have stretched the constitution's bounds.

The Senate will vote on its version of the legislation on March 4, according to Sen. Tim Kaine, one of the Democrats leading the Senate effort. The bipartisan duo of Democratic Rep. Ro Khanna and Republican Rep. Thomas Massie have introduced legislation in the House to force a vote on the Iran war.

"The American people are tired of regime change wars that cost us billions of dollars and risk our lives," Khanna said in a video statement on Feb. 28, hours after Trump launched the war. "Every member of Congress must go on record today."

The Constitution states that only Congress has the power to declare war. But Trump has launched military attacks on seven countries this term, in each case, without a green light from Capitol Hill.

The United States hasn't officially declared war since World War II. But experts say the new war in Iran could be the nail in the coffin, effectively ending Congress' unique constitutional authority to declare war.

"If Congress doesn't step up here, then we've really crossed the Rubicon in a way that we haven't seen in the past," said Tess Bridgeman, a former National Security Council advisor under President Barack Obama.

Iran war powers vote likely to fail

In a letter of notification sent to Congress on March 2 and shared by CBS and other media outlets, Trump argued Iran's sponsorship of "terrorism" and missile stockpiles "pose a direct threat" to the United States that "became untenable."

"It is not possible at this time to know the full scope and duration of military operations that may be necessary."

It's unlikely that enough Republicans will cross the aisle to vote for a War Powers Resolution, a measure that would rein in the Trump administration's three-day-old war in Iran. A handful of Republican senators shied away from taking a stand in January from an effort led by Kaine to stop Trump from further involving the U.S. military in Venezuela after the U.S. military captured Nicolás Maduro, the country's president.

Sens. Todd Young of Indiana and Josh Hawley of Missouri initially voted to advance the measure, only to flip during a mid-January vote amid pressure from the administration. The resolution failed to pass.

The War Powers Resolution holds that presidents must alert Congress to any use of U.S. military force within 48 hours. Then, they have a 60- to 90-day window before they must get congressional support – or call it off.

Trump's ongoing strikes on boats in the Caribbean and eastern Pacific, which began in September and have killed at least 140 people from Colombia, Venezuela and Ecuador, among other countries, have already blown well past that time limit.

In a notification sent to some members of Congress in October, Trump argued that the United States is in a "non-international armed conflict" with drug cartels, and that their drug trafficking constitutes "an armed attack against the United States." The administration has failed to provide any evidence that the people killed in the attacks were attempting to bring drugs into the country, and legal experts have taken umbrage at the assertion that drug traffickers can be considered armed combatants.

Trump doesn't 'bother asking' for Congress' approval

Trump's flouting of Congress' authority to declare war comes on the heels of past precedent. His predecessors stretched the bounds of constitutional law for years, balking at requirement that a commander in chief seek congressional approval.

"It just makes extremely obvious and clear something that's been true for quite some time," said Timothy Edgar, a national security lawyer who served in the Office of the Director of National Intelligence. "The president is not constrained by the Constitution and has not been for a long time."

Congress enacted the first War Powers Resolution in 1973 amid concerns in Washington that the Korean War and the Vietnam War – both started without an official war declaration – had stretched the president's power to singularly wield military force to a worrisome degree. Revelations in the late 1960's and early 70's that President Richard Nixon had ordered the secret bombing of two neutral countries, Cambodia and Laos, pushed Congress to action. Nixon vetoed the 1973 legislation, but Congress overrode it.

For more than half a century, presidents have launched numerous military attacks around the world without a formal congressional war declaration, ranging from President Bill Clinton's bombing of Yugoslavia to President Barack Obama's air assault on Libya.

After the Sept. 11 attacks, Congress authorized President George W. Bush to use the military against countries and terrorist groups the president deemed responsible. In the decades since, multiple presidents have relied on that congressional mandate to justify a grab bag of military counterterrorism activities, including the detention of people who had not been convicted of a crime at Guantanamo Bay and the secret wiretapping of Americans.

Congress has repeatedly tried to re-exert its authority in recent years to no avail.

In Trump's first term, both the House and Senate passed resolutions to stop him in 2019 from indefinitely using the military to back Saudi Arabia's war in Yemen, and in 2020, from launching a larger attack on Iran after he ordered the killing of a top general in the country's military. Trump waved away both resolutions with a presidential veto.

But at this point, the line between an all-out war that requires Congress to weigh in versus a limited use of the military outside the scope of a war is "political," not "legal," said Edgar, who gave testimony for the American Civil Liberties Union on the post-Sept. 11 authorization for the use of military force. The effect of that, he said, is that "the president can do what he likes."

Trump is the first president to "not even bother asking, or even making a case to the American public about the need for military action," he said.

Bridgeman said: "If this isn't a war in the constitutional sense, nothing is anymore."