No one expected much progress from this past week’s diplomatic marathon to defuse the security crisis Russia has ignited in Eastern Europe by surrounding Ukraine on three sides with 100,000 troops and then, by the White House’s accounting, sending in saboteurs to create a pretext for invasion.

But as the Biden administration and NATO conduct tabletop simulations about how the next few months could unfold, they are increasingly wary of another set of options for President Vladimir V. Putin, steps that are more far-reaching than simply rolling his troops and armor over Ukraine’s border.

Mr. Putin wants to extend Russia’s sphere of influence to Eastern Europe and secure written commitments that NATO will never again enlarge. If he is frustrated in reaching that goal, some of his aides suggested on the sidelines of the negotiations last week, then he would pursue Russia’s security interests with results that would be felt acutely in Europe and the United States.

There were hints, never quite spelled out, that nuclear weapons could be shifted to places — perhaps not far from the United States coastline — that would reduce warning times after a launch to as little as five minutes, potentially igniting a confrontation with echoes of the 1962 Cuban Missile Crisis.

“A hypothetical Russian invasion of Ukraine would not undermine the security of the United States,” said Dmitry Suslov, an analyst in Moscow who gave a closed-door presentation on the standoff to Russian lawmakers last month. “The overall logic of Russian actions is that it is the U.S. and NATO that must pay a high price.”

And as Ukrainians were reminded anew on Friday, as the websites of the country’s ministries were defaced in a somewhat amateurish attack, Russia’s army of hackers can wreak havoc in Ukraine, but also in power grids from Munich to Michigan.

It could all be bluster, part of a Kremlin campaign of intimidation, and a way of reminding President Biden that while he wants to focus American attention on competing and dealing with China, Mr. Putin is still capable of causing enormous disruption.

The Russian leader telegraphed that approach himself by warning repeatedly in the past year that if the West crossed the ever-shifting “red line” that, in Mr. Putin’s mind, threatens Russia’s security, he would order an unexpected response.

“Russia’s response will be asymmetrical, fast and tough,” Mr. Putin said last April, referring to the kinds of unconventional military action that Russia could take if adversaries threatened “our fundamental security interests.”

The current crisis was touched off by the Kremlin’s release of a series of demands that, if the U.S. and its allies agreed, would effectively restore Russia’s sphere of influence close to Soviet-era lines, before NATO expanded into Eastern Europe. It has also demanded that all U.S. nuclear weapons be withdrawn from Europe, saying it felt threatened by their presence — though the types and locations of those weapons haven’t changed in years. And it wants a stop to all Western troop rotations through former Warsaw Pact states that have since joined NATO.