Not much else can be done immediately, unless you're willing to gamble a nuclear war by imposing an NFZ on Ukraine. We failed to back Ukraine when it mattered. We are paying for it now.
But avenging them is within our power.
Cut Russia out of the world economy, end their access to SWIFT, round up the oligarchs in London, Paris, Brussels and Florida, send them packing home.
Step up NATO forward deployments to the Baltic countries, reopen permanent basing for US, British and Canadian assets in Germany, extend invitations to Sweden, Finland and Moldova so that wherever Putin looks west of Ukraine, there is a NATO fist waiting.
Arm the insurgency in Ukraine, recognize the Ukrainian government in exile, increase our media penetration in Russia, conduct offensive cyberwarfare operations to cripple oil and gas infrastructure, destabilize Putin's gangster regime and let ordinary Russians bring down the man who led them to ruin.
Ukraine is our failure, but we can make damn sure that another Ukraine is made utterly impossible, and that Putin suffers for his actions today.