A month ago, Russian President Vladimir Putin appeared to be successfully executing his campaign to destabilize Ukraine. While Russian-backed insurgents consolidated a breakaway republic, weak and divided Western governments ignored their own deadlines for imposing sanctions.

Now, suddenly, Putin faces twin reversals: relatively tough sanctions from the United States and European Union on Russian banks and oil companies, and a string of military defeats that have pushed back his proxy forces. It’s a dangerous moment for Putin – and, perhaps, an opportunity for Ukraine and its allies.

Ukrainian officials, like some of their counterparts in the West, worry about a reckless lashing out by a ruler who feels cornered. Putin, they counsel, still should be offered a face-saving way of retreating from Ukraine. President Petro Poroshenko and the interim government, which have been offering such compromises all along, are set to renew negotiations with the Russian-backed forces this week.

Russia should not be allowed to permanently entrench its proxy forces in eastern Ukraine, creating a “frozen conflict.”

The West also should not shrink from the destabilization of Putin’s regime. Once considered a partner, this Kremlin ruler has evolved into a dangerous rogue who threatens the stability and peace of Europe. If he can be undermined through sanctions and the restoration of order in eastern Ukraine, he should be.