WASHINGTON (AP) — President Joe Biden does not plan to respond to a new Russian invasion of Ukraine by sending combat troops. But he could pursue a range of less dramatic but still risky military options, including supporting a Ukrainian resistance after the invasion.

The reason for not directly joining a Russian-Ukrainian war is simple. The United States has no treaty obligation to Ukraine, and a war with Russia would be a huge gamble, given its potential to expand into Europe, destabilize the region, and escalate to the frightening point of risk a nuclear exchange.

Doing too little also carries risks. This could suggest acquiescence to future Russian actions against other Eastern European countries, such as the Baltic states of Estonia, Latvia and Lithuania, although as members of NATO these three countries have security guarantees from the United States and the rest of the alliance.

Secretary of State Antony Blinken, who is in Europe this week meeting with Ukrainian officials, consulting with NATO allies and then meeting his Russian counterpart on Friday, affirmed “an unwavering commitment by the United States to the sovereignty and territorial integrity of Ukraine”. But he has not publicly defined the limits of this commitment.

How far could the United States and its allies go to help Ukraine defend itself if the Russian force buildup along the borders of Ukraine leads to an invasion?

WHY NOT CONTEST A RUSSIAN INVASION?

Going to war against Russia in Ukraine could tie up American forces and resources for years and cause many casualties with an uncertain outcome at a time when the Biden administration is trying to focus on China as the main threat to the security.

On Wednesday, Biden said it was his “guess” that Russian President Vladimir Putin would eventually send forces to Ukraine, although he also said he didn’t think Putin wanted all-out war. Biden did not raise the possibility of sending US ground troops to Ukraine to stop an invasion, but he had previously ruled it out.

Biden said he doesn’t know how Putin will use the forces he has amassed near the Ukrainian border, but the US and NATO have rejected what Moscow calls its main demand — a guarantee that the western alliance will not extend further east. Russia annexed the Crimean peninsula to Ukraine in 2014 after the ousting of the pro-Moscow Ukrainian leader and also intervened in eastern Ukraine that year to support a separatist insurgency. More than 14,000 people have been killed there in nearly eight years of fighting.

The stakes in Ukraine are high – militarily and politically. Lawmakers have stepped up their criticism of Biden’s approach to Putin. Sen. James Inhofe of Oklahoma, the ranking Republican on the Senate Armed Services Committee, accused Biden of “twisting and appeasement,” but he did not urge sending combat troops. Rep. Jim Himes, a Connecticut Democrat who serves on the House Intelligence Committee, called for an urgent “nonstop airlift” of military hardware and trainers to Ukraine.

Philip Breedlove, a retired Air Force general who served as NATO’s top commander in Europe from 2013 to 2016, said in an interview that he neither expected nor recommended that the United States is sending combat troops to Ukraine. Instead, Washington and its allies should seek ways to help Ukraine defend its own airspace and territorial waters, where it faces overwhelming Russian superiority, he said.

“These are things that we should consider as an alliance and as a nation,” he said. “If Mr. Putin is allowed to invade Ukraine and there are little or no consequences, we will see the same thing.”

WHAT ARE BIDEN’S OTHER OPTIONS?

Given its marked military inferiority, Ukraine was unable to prevent Russian forces from invading. But with help from the United States and others, Ukraine could dissuade Putin from acting if he was convinced the costs would be too high.

“The key to thwarting Russian ambitions is to prevent Moscow from having a quick victory and increasing the economic, political and military costs by imposing economic sanctions, ensuring political isolation from the West and evoking the prospect of a protracted insurgency that draws away from the Russian military,” political scientist Seth Jones and former CIA paramilitary officer Philip Wasielewski wrote in a Jan. 13 analysis for the Center for Strategic and International Studies. .

The Biden administration has hinted that it is thinking along the same lines.

HOW IS THE US SUPPORTING THE UKRAINE ARMY NOW?

Pentagon press secretary John Kirby said there were about 200 National Guard troops in Ukraine to train and advise local forces, and on Tuesday he said there were no plans to increase their number. There are also an undisclosed number of US special operations troops training in Ukraine. Kirby did not say whether US soldiers would withdraw in the event of a Russian invasion, but he said the Pentagon would “take all appropriate and proper decisions to ensure that our people are safe in any event.”

The administration said Wednesday it would provide an additional $200 million in defensive military aid to Ukraine. Since 2014, the United States has provided Ukraine about $2.5 billion in defense assistance, including anti-tank missiles and radar.

HOW COULD THE US HELP UKRAINE AFTER AN INVASION?

It’s not clear. National Security Advisor Jake Sullivan said last week that the United States would “significantly step up” its support for Ukraine’s “territorial integrity and sovereignty.” But he did not specify how this could be done.

The administration also says it is open to sending military reinforcements to NATO allies on the eastern front who want reassurance from the Americans.

Jones and Wasielewski argue that in addition to implementing tough sanctions against Russia in the event of an invasion, the United States should provide Ukraine with a wide range of military assistance free of charge. This would include air, anti-tank and anti-ship defense systems; electronic warfare and cyber defense systems; small arms and artillery ammunition, and other items.

“The United States and NATO should be prepared to offer long-term support to the Ukrainian resistance, whatever form it eventually takes,” they wrote. This aid could be provided overtly with the help of US troops, including special operations forces, or it could be a covert action directed by the CIA and authorized by President Biden, they added.

It would carry the risk of placing American personnel in the line of fire – and dragging the United States into the very fight it is determined to avoid.