Rushing U.S. troops to Europe, issuing economic sanctions and sending more lethal weaponry to Ukraine are among the options President Joe Biden is considering as Russia masses troops on Ukraine’s border.The moves aim to deter Russian President Vladimir Putin from invading Ukraine, and, if he does, to make him pay a price by facing a well-armed adversary.

Russian President Vladimir Putin attends a meeting with the governor of the Kamchatka Territory at the Kremlin in Moscow on Monday.Russian President Vladimir Putin attends a meeting with the governor of the Kamchatka Territory at the Kremlin in Moscow on Monday.Biden’s approach to the crisis depends on Putin’s next moves in eastern Europe, experts say. If Putin is bluffing a full-scale invasion in order to rattle allies and prevent Ukraine from joining NATO, then a U.S. response limited to sanctions and more lethal aid to Ukraine is warranted. A Russian invasion of Ukraine could shatter the alliances that have maintained peace and prosperity in Europe. That would demand a far more robust response, according to former Defense Secretary Chuck Hagel.

“I’m not saying go to war with Russia directly,” Hagel said. “But he (Putin) is going to have to pay a very, very high price. Not just from us, but from every European country. Or this won’t be the last time he does it.”

Putin’s deployment of more than 100,000 troops to Russia’s border and plans for military exercises in Belarus, a short distance from Kyiv, have heightened tension between the U.S. and its European allies and Russia. Putin has sought to regain influence in countries once part of the Soviet Union and prevent the NATO alliance from extending to Ukraine. The United States has supported Ukraine, a democracy that has sought closer ties with the West.

The crisis has rattled America’s NATO allies and the Pentagon, which alerted 8,500 troops on Monday to prepare for swift deployment to Europe. NATO also announced the deployment of more troops and equipment to the alliance’s eastern front.

Hagel called the crisis the worst in Europe since the height of the Cold War and compared Putin’s aggression to that of Adolph Hitler prior to the outbreak of World War II.

US ready to beef up arms in Ukraine

Hagel and others, such as Sen. Richard Blumenthal, D-Conn., a member of the Armed Services Committee, advocate expanding military aid to Ukraine beyond what has been mostly shipments of small arms. Since Putin annexed the Crimean peninsula in 2014, more than $2.5 billion in U.S. military aid and training has been sent to Ukraine.

On Friday, the State Department authorized Baltic allies to supply Ukraine with American-made anti-aircraft missiles, ratcheting up the risk to Russia helicopters and other aircraft, according to a statement from the Estonian Defense Ministry.

At a meeting with Biden last week, officials discussed how to counter Russia’s military buildup on Ukraine’s borders, according to Blumenthal, who visited Ukraine recently as part of a congressional delegation. Tougher economic sanctions and increased military aid were among the topics discussed at the White House, he said.

This handout photo courtesy of US Air Force taken on Friday shows Senior Airman Zachary Kline, 436th Aerial Port Squadron cargo processor, palletizes ammunition, weapons and other equipment bound for Ukraine during a foreign military sales mission at Dover Air Force Base, Delaware.This handout photo courtesy of US Air Force taken on Friday shows Senior Airman Zachary Kline, 436th Aerial Port Squadron cargo processor, palletizes ammunition, weapons and other equipment bound for Ukraine during a foreign military sales mission at Dover Air Force Base, Delaware.“A range of other kinds of arms” are under consideration, Blumenthal said. He declined to detail the nature of the weaponry, citing secrecy concerns.

Should Putin order an invasion of Ukraine, military support from the west would have to be increased substantially, Hagel said. More sophisticated weaponry, not U.S. troops, should be sent.

More U.S.-made weaponry will be sent to Ukraine should Russia attack, according to a State Department spokesman who was not authorized to speak publicly.

Since 2014, the Pentagon has supplied the Ukrainian military with a variety of equipment, such as radios, vehicles, patrol boats and some defensive weaponry, including Javelin anti-tank missiles and small arms, including machine guns. Other western allies have provided similar equipment.

Ukrainian troops are now better trained than eight years ago, Hagel said. Pentagon officials will have to determine what type of offensive weapons and vehicles they could operate and maintain, he said. If Ukrainian troops are capable of handling them, the Pentagon should consider sending armored personnel carriers, drones and even tanks.

The risk of being drawn deeper into such a conflict is outweighed by the cost of encouraging Putin’s aggression, Hagel said.

US eyes positioning troops in Europe – but not Ukraine

Biden has said the U.S. would not send troops to help defend Ukraine, but the president said last week the U.S. would likely send more American forces to other eastern European countries, including Poland and Romania. There is a small contingent of National Guard troops in Ukraine on a regular training mission.

On Monday, the Pentagon announced that 8,500 U.S. troops had been put on heightened alert to deploy to Europe as part of a NATO quick reaction force. Infantry, aviation, intelligence and surveillance units are among those that could be dispatched in as quickly as five days, said John Kirby, the Pentagon press secretary.

They would be sent to NATO-member countries but not Ukraine.

Pentagon spokesman John Kirby speaks during a briefing at the Pentagon in Washington on Monday. The Pentagon says that Defense Secretary Lloyd Austin has put about 8,500 troops on heightened alert, so they will be prepared to deploy if needed to reassure NATO allies in the face of ongoing Russian aggression on the border of Ukraine. Pentagon spokesman John Kirby speaks during a briefing at the Pentagon in Washington on Monday. The Pentagon says that Defense Secretary Lloyd Austin has put about 8,500 troops on heightened alert, so they will be prepared to deploy if needed to reassure NATO allies in the face of ongoing Russian aggression on the border of Ukraine.

Putin appears less intent on invading Ukraine than preventing it from joining NATO, said Michael O’Hanlon, a military expert at the Brookings Institution. Ukraine’s admission to NATO remains a distant prospect, and Putin aims to foreclose it entirely, he said.

“I suspect deterrence will work – provided we don’t actually move towards membership in NATO for Ukraine,” O’Hanlon said. “I don’t think we should threaten to fight over Ukraine. But if he did attack, and I was wrong, I believe the West needs a credible strategy to wean itself off Russian gas and oil long-term.”

Russia’s more than 100K border troops pose threat

The crisis in eastern Europe has been brewing for weeks as Putin has mobilized more than 100,000 troops to Russia’s border with Ukraine. Russia has defended its right to deploy forces within its borders. It also denies U.S. assertions made last week that it has sent operatives into Ukraine to spark a crisis that it could then use to justify a military invasion.

Russia has been demanding security concessions from the United States and its European allies, including guarantees that the NATO alliance will not foster closer military ties with Ukraine or other eastern European countries.

Russia’s troops, armor and aircraft would quickly overwhelm Ukrainian forces, according to a U.S. official who was not authorized to comment. But senior Defense Department officials have warned their Russian counterparts that Ukrainian troops and paramilitary forces have the capability to fight a bloody, protracted insurgency.

Russia has announced military exercises in neighboring Belarus next month. Troops massed there could pour into Ukraine and be just hours from Kyiv, the Ukraine capital, Blumenthal said. Those forces would have to wait for the ground to freeze in order to support armored vehicles. That could happen in a matter of weeks, according to Blumenthal and other officials.

The U.S should be prepared to equip Ukrainian forces with weaponry to replicate the quagmire that Russia found itself in after invading Afghanistan in 1979, Blumenthal said. Russian forces withdrew 10 years later after fighting an insurgency supported in part with U.S. arms. The CIA supplied Afghan insurgents with shoulder-fired anti-aircraft Stinger missiles used to bring down Russian helicopters.

The announcement by Estonia that it will provide Javelin missiles, while Latvia and Lithuania will provide Stingers, bolsters Ukraine’s defenses significantly.

“The Ukrainians are organizing to resist an invasion,” Blumenthal said. “Putin needs to know he will face another Afghanistan. That’s one option for deterring him.”