The Obama administration was widely derided for “leading from behind” during the crisis in Libya. To address the evolving conflict in Ukraine, President Obama has to lead from out front and convince allies that the stakes are too high to let Russian President Vladimir Putin get away with territorial aggression.

There’s no justification for Putin’s invasion of Crimea or his threat to take action in other parts of Ukraine that have a high number of ethnic Russians or business interests affecting Russia. In fact, his government’s action in Crimea violates international law. Unlike some gray international issues, this is a black-and-white case, and Russia must be held accountable.

Obama’s test is to quickly convince global leaders to join the United States and use maximum diplomatic and economic leverage to make it clear to Putin that Crimea is not worth the cost.

In doing so, Obama needs to avoid the empty threats he used regarding Syria, where his self-described “red line” blurred despite that regime’s proven use of chemical weapons. All options are not on the table: Russia’s nuclear stockpile means a hot war must be avoided even while the Cold War reheats. But there are other ways to pressure Putin, and Obama should make full use of them.

Diplomatically, the Sochi Olympics proved that global prestige is a clear Putin objective. Russia should be diplomatically isolated. The planned G-8 Summit in Sochi should be boycotted and, unless its troops stand down, Russia should be booted from the G-8 altogether.

Diplomatic institutions like the United Nations should play a role, too. Sure, Russia has a permanent veto in the U.N. Security Council. And its representatives should be forced to use it — again and again.

There are promising signs that the Obama administration is stepping up. Bilateral military and trade talks have been suspended. And reportedly, several options are already being explored that would target Russian institutions and individuals, such as freezing assets and banning visas.

Sanctions that would restrict access to portions of the international banking system should be considered, too. Russian government officials and the crony capitalists who benefit from Putin’s regime should be squeezed to the point that key supporters urge reconsideration of Putin’s policies, if not his continued governance.

The key will be to make these moves multilateral. Some critically important Western leaders are reportedly less willing to impose tough economic conditions on Russia. Because Western Europe’s economic ties are much greater than America’s, Putin will face less pressure if there is not significant disruption in his country’s dealings with Germany, Great Britain, France and other leading European economies.

Obama also needs to prepare allies and the American people for the realization that there will be economic costs to containing Putin. On a Tuesday visit to Kiev, Secretary of State John Kerry pledged $1 billion in loan guarantees to Ukraine’s fledgling government. More aid surely will be needed, especially if Russia uses its economic leverage of oil and gas. Twice before, Russia has used energy as a weapon against Ukraine, and it’s likely to do so again.

Russia’s ruble, stock market and interest rates are already experiencing blowback out of fear of some kind of collective action. An aggressive and unified response could exacerbate these trends and help convince Putin to reconsider his bellicosity. On Tuesday, he seemed to back off from a major escalation, but the crisis is clearly not over.

On its own, the showdown in Ukraine is enough to coalesce global leaders. But because Russia also plays a key role in diplomacy regarding Iran, North Korea, Syria and other troubled regions, it’s essential that Putin not be emboldened to dictate terms of those negotiations, too.

Putin considers the breakup of the Soviet Union “the greatest geopolitical catastrophe of the [20th] century.” Intimidating Ukraine doesn’t reconstitute the USSR. Instead, it damages modern-day Russia — a fact that needs to be made clearer to Putin.