Cut off Russian gas and oil completely for starters, go after all Russian investments in the West, refuse to do business with any company in Russia, no more boats in and out of Russia, no more cargo, refuse to do business with companies from other countries that continue to do business in Russia, gift major arms and training to Ukraine on the assumption that this war isn't going to be over in a week.

Putin will see his reasons for escalation wherever he wants, whatever will suit him, if that becomes the touchstone then we are already way across the line regardless of our fears. After all, we exist.