TAKEN BY surprise by the Russian occupation of Crimea, President Obama has rebounded strongly. He has led Western nations in condemning Russian President Vladi­mir Putin’s move as a violation of international law. Mr. Obama signed an order clearing the way for U.S. financial sanctions against Russian individuals and businesses before the European Union met to consider its response — a step that strengthened the position of Europeans calling for tough E.U. steps.

The president has been on the phone not just to Mr. Putin and customary counterparts including German Chancellor Angela Merkel but also to the leaders of China, Spain, Kazakhstan and the Baltic states. On Wednesday he will meet interim Ukrainian Prime Minister Arseniy Yatsenyuk at the White House, a step that is particularly significant because Mr. Yatsenyuk’s government has not been recognized by Moscow.

In short, no one can fairly accuse Mr. Obama of “leading from behind” on Crimea. Thanks to the president’s efforts and Mr. Putin’s intransigence — he has refused multiple offers of mediation — the United States appears poised to join with Europe in imposing significant economic sanctions on Russia if it continues to move toward annexing the region or invades other parts of Ukraine.

If they are sufficiently robust, those sanctions have the potential to do serious damage to Mr. Putin’s regime. Oligarchs close to the Russian ruler have billions stashed in banks and invested in real estate in the West. The Russian navy is awaiting delivery of French-built ships. Crimea, meanwhile, gets almost all of its water, energy and food from within Ukraine. If the border were closed, Russia, which lacks a land bridge to Crimea, would find it hard to prevent an economic collapse there.

It is simply not true, as some defeatists suggest, that the West does not have the potential to force a Russian change of course. The real question is whether Western leaders are prepared to accept the damage to their own citizens and economies that would be the side effect. Russia would probably freeze Western investments on its territory; it might cut off gas exports to Ukraine, through which supplies to several E.U. countries flow. Seventy percent of Russian exports are oil and gas, most of which go to Europe.

With elections approaching in both the European Union and the United States, it will be easy to shrink from measures that would command Mr. Putin’s attention. Clearly he is counting on such a reaction. But the price of failing to take robust steps now will, in the end, be higher. If Mr. Putin is not stopped in Crimea, he will set his sights on other parts of Ukraine and maybe other former Soviet bloc states with Russian minorities. That could lead not just to economic disruption but also to war.