Isolating Russia economically would entail quarantining, for example, the gas sector and the world’s largest gas producer, Gazprom.
Gazprom is Europe’s biggest gas supplier. The US would be barely affected by such sanctions. Europe and Germany would be hammered.
All of the Baltic, central and eastern Europe, including Ukraine itself, are utterly dependent on Gazprom, while Germany, Europe’s biggest energy consumer, gets more than one-third of its gas from Russia.
More likely is also Yugoslav-style Western mediation, with “contact groups” of diplomats or UN envoys charged with running negotiations between the warring parties, monitoring ceasefires and dispatching observers under the UN or the Organization for Security and Co-operation in Europe.