It’s time for President Obama to start using the I-word when referring to Russia’s assault on Ukraine. I mean invasion.

The world is witnessing a Russian invasion of a neighboring country, something that hasn’t happened since the fall of the Soviet Union (except for Russia’s 2008 invasion of Georgia).

As U.S. Air Force Gen. Philip Breedlove, NATO’s top commander, stated bluntly: “Russian tanks, Russian artillery, Russian air defense systems, and Russian combat troops” have been moving into Ukraine. Repeatedly. “What worries me the most,” Breedlove said in Bulgaria, is that the Russia-Ukraine border is “completely porous. (Russian) forces, money, support, supplies, weapons are flowing back and forth across this border completely at will.”

Yet so far, neither the president nor his European allies have been willing to call this influx an invasion. U.S. officials fear that using the I-word would provoke Vladimir Putin.

In fact, the opposite is true. Unless the West stops pussyfooting around Putin, the Russian leader will complete his project of dismembering Ukraine and threaten other European states.

Of course, there’s a political reason for the West’s word games. “If they say it’s an invasion, it would make people ask, ‘Why aren’t you doing more?’ ” said the Atlantic Council’s John Herbst, a former U.S. ambassador to Ukraine, “especially since this is happening in the heart of Europe.”

Washington and the European Union have imposed economic sanctions on Moscow, which have hurt a Russian economy reeling from low oil prices, but haven’t moved Putin. U.S. and European officials have clung to the hope that sanctions will impel Putin to abide by the Minsk accord, a September deal between Kiev and Moscow. The accord was supposed to guarantee the sanctity of Ukraine’s borders while ensuring that Russian-speakers in Ukraine’s east gain autonomy and language rights — something Kiev was willing to grant.

However, Russia has violated the Minsk accords from the start.

Putin has sent arms, troops and hundreds of military trainers across into Ukraine to create a proxy army in the east. Its goal: to separate the Donbass region from the rest of the country and link them to Russia. Many of the fighters are Russian citizens or intelligence agents who enter Ukraine in unmarked uniforms and vehicles.

Putin has recognized a fake “elected government” in those two districts — a gross violation of the Minsk accord. He demands that Kiev negotiate with these proxies rather than their handlers in Moscow. Kiev rightly refuses.

All the while, Putin, his officials, and the Russian media lie with straight faces about this, just as they did about the Russian “green men” who invaded and occupied Crimea earlier this year. By refusing to confront Putin about his current invasion of eastern Ukraine, the West helps him sustain the fiction that his proxy war is a spontaneous revolt.

There is a ton of evidence to the contrary, even beyond what the West has collected from satellite photos. A few examples: European monitors, as well as Western and Russian journalists, have seen Russian military convoys cross the border, and convoys of dead Russian soldiers’ bodies cross back. Russian journalists and solders’ rights groups have reported on secret burials of repatriated casualties.

One Moscow contact told me of a friend’s son, a Russian contract soldier wounded in Ukraine, who is being forced to accept treatment at a remote regional hospital rather than in Moscow because the government wants to keep the casualties secret.

So it’s past time that the White House started talking publicly about the Russian invasion of Ukraine. And once the I-word is used, it’s also time for Obama to rethink his refusal to send defensive weapons to Ukraine. If he won’t act, Congress should.

U.S. officials argue that there is no military solution to the Ukraine conflict. But Putin hasn’t gotten that message. Russia is building up its forces on the Ukraine border and looks ready to seize a land corridor in southern Ukraine to link Russia to Crimea.

“If you send arms now, it might keep Putin from making the next land grab,” said Herbst. “Not giving arms increases the risk, increases the chance of escalation.”

In other words, the only thing that may make Putin think twice and return to diplomacy is if the cost of an escalated invasion will be too high, including the risk that his public will learn about casualties.

It’s time to stop enabling Putin by refusing to call his invasion by its rightful name.

Trudy Rubin is a columnist for the Philadelphia Inquirer.