WASHINGTON (AP) — With rare but fragile alignment, the U.S. Congress is largely backing President Joe Biden's decision to confront Russia with potentially escalating sanctions for the crisis in Ukraine as lawmakers brace for perhaps the most daunting foreign policy crisis the nation has faced in a generation.

But the next steps are highly volatile — even more so after Russian President Vladimir Putin announced early Thursday a military operation in Ukraine and explosions were heard in Kyiv, Kharkiv, Odessa and other cities there.

"We must refuse to stand by and watch innocent Ukrainian men, women, and children suffer," the chairman of the Senate Foreign Relations Committee, Sen. Bob Menendez, D-N.J., said in a statement after Putin's forces moved against Ukraine. He said he was "committed to ensuring that the United States upholds our responsibility to exact maximum costs on Putin, the Russian economy, and those who enabled and facilitated this trampling of Ukraine's sovereignty."

With isolationist impulses rising at home, Congress has no appetite for war. Yet Americans also appear ambivalent about the U.S. working to keep the peace. New polling from The Associated Press and NORC — taken before Putin's announcement — says just 26% of Americans want the U.S. to play a major role in the Russia-Ukraine conflict.

House Speaker Nancy Pelosi said Wednesday that Russia's aggression toward Ukraine is "an attack on democracy," vowing that the U.S. will stand united with its allies around the world in swiftly imposing sanctions on Russia and ensuring financial and political support for an independent Ukraine.

Pelosi, who returned to the Capitol from a diplomatic overseas trip, situated the aggression from Russia toward Ukraine alongside intervention in the United States' own democratic process during the 2016 election.

"There will be a price to pay for Vladimir Putin," she said, flanked by lawmakers who had joined her delegation at the annual security conference in Munich.

While Republican critics of the Biden administration — and even some Democrats — want the White House to go even tougher with swifter and more severe sanctions on Russia, most have given varying degrees of support for the White House strategy, including Biden's move Wednesday to sanction the company building the Russia-to-Germany Nord Stream 2 gas pipeline.

The top Republican on the Foreign Relations Committee, Sen. Jim Risch of Idaho, said sanctions on Nord Stream 2 are "long overdue, but I cannot overstate how critical they are to showing Putin that violating a nation's sovereignty has consequences."

Risch, who has worked with colleagues on a bipartisan basis for years trying to end the pipeline, said: "It is good to see President Biden do the right thing."

Republican leaders have sought to steer the conversation to their preferred terms, as the party whose defense hawks once led the nation on the national security front. But it's not at all clear whether today's GOP can keep Republicans from tapping into an impassioned non-interventionist strain unleashed by Donald Trump's "America First" approach.

It was Trump who sought to strip protections for Ukraine from the Republican Party platform for the 2016 election, and who was impeached by the House for abuse of power after he pressured the Ukrainian president to dig up dirt on Biden ahead of the 2020 campaign.

This week, Trump cheered on Putin as he massed military forces near Ukraine's border and recognized the independence of its separatist regions in a move Biden and others warned was the start of an invasion of Ukraine. As president, Trump had been critical of NATO, working to distance the U.S. from the historic partnership and berating allies to contribute more money to defense.

Senate Republican leader Mitch McConnell, a longtime champion of NATO, spoke highly of the Western alliance this week, but some within his party are gravitating away from that traditional Republican position and toward Trump's views.

McConnell said he wants to see Biden impose the "toughest possible sanctions."

Other Republicans, though, most notably Sen. Josh Hawley of Missouri, a potential Republican presidential hopeful, has said the U.S. should be paying closer attention to the greater challenges he believes are posed by China.

Still, most Republican senators are backing Biden's sanctions on Putin, even if some are clamoring for more and taking political punches at Biden for seeming too tepid.

Republican Sen. Lindsey Graham of South Carolina, a sometimes Trump ally who is also one of the party's leading defense hawks and who used to globetrot with fellow GOP Sen. John McCain, invoked his late colleague this week in urging Biden to confront Putin more forcefully.

Graham said Congress should impose "sanctions from hell" on Putin and his regime when lawmakers return to work next week.

Sen. Ted Cruz, who had single-handedly blocked Biden's nominees for various State Department posts to halt the Russia-to-Germany pipeline, said with the announced new sanctions he would lift his blockade. "President Biden has now taken positive steps," Cruz, R-Texas, said in a statement. "But much more still needs to be done to deter and counter the threat that Putin poses to our allies in Ukraine and across Europe."

Pelosi said Russians need to understand what their leader is doing. "It's stunning to see in this day and age a tyrant roll into a country," Pelosi said. "This is the same tyrant who attacked our democracy in 2016,"

It's unclear what more, if anything, Congress will do to confront Russia, as lawmakers hold back their own legislative response to Putin while Biden engages U.S. allies in a more global strategy.

The Senate has bipartisan support for a robust sanctions package but after running into differences over the scope and timing of the response decided to shelve a vote as the White House pursued its own approach.

Graham has suggested a supplemental spending package for Ukraine, which already receives money and defensive equipment from the U.S., but it does not yet appear that additional funds are being considered.

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Associated Press writer Farnoush Amiri contributed to this report.

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This story has been corrected to say that Trump pressured the Ukrainian president ahead of the 2020 campaign.