Lawmakers from both political parties weigh in on President Trump's decision to order airstrikes in Syria on April 6, in retaliation for a chemical attack on civilians. Many senators lauded the attacks as "proportionate," but split on what Trump's next steps should be. (Bastien Inzaurralde,Jenny Starrs/The Washington Post)

To hear Sen. Marco Rubio (R-Fla.) and other top Senate Republicans review President Trump's two very different reactions to a deadly chemical attack in Syria this week is to hear them talk about two completely different presidents.

The noninterventionist president they despised. The first president to launch direct military strikes into Syria during its civil war — now this is a president they can get behind.

“Tonight's actions show the days of being able to attack with impunity when it comes to Assad are over," Rubio said to CNN's Anderson Cooper.

A few days ago, Trump's administration seemed content to let Syrian President Bashar al-Assad stay in power. Days before the chemical attack, Secretary of State Rex Tillerson said Assad's fate is in the hands of his people. And on Wednesday, Rubio accused Tillerson of providing the “incentive” for Assad to allegedly launch a chemical weapon attack on his own people.

Washington Post reporter Dan Lamothe explains why President Trump launched 59 Tomahawk missiles at a Syrian military airfield on April 6 and what this means for the fight against the Islamic State. (Sarah Parnass,Julio Negron/The Washington Post)

On Thursday night, the president launched more than 50 missiles at Assad's government. “It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons,” Trump said in a somber statement from his Mar-a-Lago estate in Florida.

This wasn't just a notable shift for a president attracted to the idea of stepping America back from global affairs. This would be a major moment for any U.S. president. Thursday's missiles launched at a Syrian military airfield was the first direct American military assault on Syria's government in that country's six-year-long civil war.

And senior Republicans who have been Trump antagonists on foreign policy loved it.

“Unlike the previous administration, President Trump confronted a pivotal moment in Syria and took action,” Sens. John McCain (R-Ariz.) and Lindsey O. Graham (R-S.C.) said in a joint statement.

Even top Senate Democrats weren't immediately critical. Here's a statement from Sen. Richard J. Durbin (Ill.), the No. 2 Senate Democrat: “My preliminary briefing by the White House indicated this was a measured response to the Syrian nerve gas atrocity.”

Late Thursday night, the ultimate validation came via statement from Sen. Bob Corker (R-Tenn.), who chairs the Senate Foreign Relations Committee: “I applaud President Trump for taking decisive action following the latest chemical weapons attack. It is critical that Assad knows he will no longer enjoy impunity for his horrific crimes against his own citizens, and this proportional step was appropriate.”

It's hard to overstate how totally, completely, utterly different these Republicans' reactions to Trump's Syria policy are from earlier this week.

On CNN on Wednesday morning, McCain, chairman of the Senate Armed Services Committee and a chief Trump antagonist, characterized Tillerson's comment that Assad's fate is in the hands of Syrians as “one of the more incredible statements I've ever heard.”

Sen. Rob Portman (R-Ohio), also a member of the Senate Foreign Relations Committee, issued a statement in response to the chemical attack it seems he wished Trump had delivered. In it, a not-so-subtle prod to Trump to change his ways: “We cannot afford to make the same mistake twice.”

It's possible that Senate Republicans' loud, direct criticism of Trump put him in a tough place — or at the very least underscored the ocean between him and the core of his party on foreign policy.

As The Washington Post's Greg Jaffe wrote of Trump's worldview up until Thursday night: “The Syrian chemical weapons attack poses a particular problem for Trump’s foreign policy philosophy. The attack by Assad’s forces offends America’s values and it violates long-standing international norms of behavior, but it does not present an immediate threat to America’s security or its economic interests. In an 'America First' world, it is an atrocity, but hardly a call to action for the United States and its allies.”

By Wednesday afternoon, McCain and Rubio had fired their barbs, and Trump said vaguely in a news conference that his attitude toward Syria has “changed.” Until he launched military strikes, we weren't really sure what the president meant by that.

Now, top Senate Republicans concerned about the death, destruction and instability that a Syrian president unanswerable to the United States has caused seem greatly relieved he's come to their side.

Of course, Trump's sudden about-face on Syrian policy won't bring him closer with everyone in his party. Sen. Rand Paul (R-Ky.), whose foreign policy tends to line up with the libertarian, noninterventionist sect, reminded Trump of the fact that Congress, not the White House, has the power to authorize military force.

And Sen. Tim Kaine (D-Va.), who had made a name for himself in Congress demanding that the Obama and Trump administrations come to it for approval of military force, called the military strike "unlawful": "I voted for military action against Syria in 2013 when Donald Trump was advocating that America turn its back on Assad's atrocities. Congress will work with the President, but this failure to seek Congressional approval is unlawful."

That's a problem Trump will have to face in the coming days — one that his predecessor never quite solved. But at least he'll do it with some of the top Republican members of Congress behind him.