Newly announced American and European sanctions on Russian President Vladimir Putin's "cronies" mark a key escalation of pressure in the dispute over Ukraine and Crimea. But the move also puts President Obama in a precarious position should punishments fail to halt Russian aggression, with a public back home deeply skeptical of ratcheting things up beyond international sanctions.

Americans' reluctance was laid bare in a CNN poll last week. Obama's current policy is widely popular, with almost six in 10 supporting economic sanctions on Russia (it was 56 percent support  in a Post-ABC poll). But at least half of Americans opposed all five other potential actions asked in the survey: economic assistance to Ukraine's government (52 percent opposed), canceling an international summit (58 percent), sending weapons to Ukraine's government (76 percent), U.S. air strikes (82 percent) and ground troops (88 percent).

Why are Americans so reluctant to amp up the showdown with Russia? The CNN poll rules out sympathy for Putin's causemwith 81 percent saying Russia's actions in Crimea broke international law and 69 percent now calling the nation a threat to the U.S., up 25 points since 2012

But these concerns may be overwhelmed by a growing resistance to be the world's police force after a public souring on wars in Iraq and Afghanistan. When asked whether the U.S. should "mind its own business internationally and let other countries get along the best they can on their own," 52 percent agreed with that sentiment in a Pew Research survey last fall, the highest in nearly 50 years of polling and up sharply over the last decade.

And the conflict over Ukraine appears to be just the type of engagement Americans want to stay away from, according to an in-depth 2010 survey by the Chicago Council on Global Affairs. Just 24 percent said protecting weaker nations against foreign aggression is a "very important" foreign policy goal, ranking 18th out of 19 goals, significantly behind "combating world hunger" and "reducing our trade deficit."

Obama is keenly aware of the public's skepticism toward intervention, saying in 2011 that "the tide of war is receding" as troops came home from Iraq. But as the Post's Scott Wilson wrote earlier this month: "Ukraine has emerged as a test of Obama’s argument that, far from weakening American power, he has enhanced it through smarter diplomacy, stronger alliances and a realism untainted by the ideology that guided his predecessor."

The basic challenge Obama faces is how to force compliance from Putin in the face of such obvious public disinterest back home for escalating the situation. Obama promised Putin that aggression toward Ukraine would entail "costs," but if they are cheap, the Russian president may be willing to pay.