Biden-Putin Phone Calls Plot Shift from Ukraine 'Concerns' to NATO War Footing

Phone calls between President Joe Biden and Russia's Vladimir Putin over the past year show a shift towards a war footing over Ukraine.

Three conversations between the leaders help plot the descent from "concerns" to the real possibility of conflict.

Biden warned Putin during an hourlong call on Saturday that the U.S. and its allies will "respond decisively and impose swift and severe costs" on Russia if it invades Ukraine, according to a readout shared by the White House.

The West wanted to "engage in diplomacy," it said, but warned "we are equally prepared for other scenarios."

So, despite repeated high-profile calls and ongoing dialogue, how did relations get here?

Russia has repeatedly denied that it intends to invade its neighbor despite massing well more than 100,000 troops near the Ukrainian border.

Nearly a year has passed since Moscow's buildup of troops first sparked alarm.

In a phone call on April 13 last year, Biden emphasized America's "unwavering commitment to Ukraine's sovereignty and territorial integrity," according the White House.

"The President voiced our concerns over the sudden Russian military build-up in occupied Crimea and on Ukraine's borders, and called on Russia to de-escalate tensions," it added.

Biden also reaffirmed his goal of building "a stable and predictable relationship" with Russia and proposed a summit meeting in a third country during that call.

But by December, tensions between Russia and Ukraine had escalated significantly prompting Biden to warn Putin of sweeping economic sanctions in a bid to deter Russia from invading Ukraine.

Biden "voiced the deep concerns of the United States and our European Allies about Russia's escalation of forces surrounding Ukraine and made clear that the U.S. and our Allies would respond with strong economic and other measures in the event of military escalation," according to a readout of a Biden-Putin video call on December 7.

Biden also "reiterated his support for Ukraine's sovereignty and territorial integrity and called for de-escalation and a return to diplomacy," according to the readout.

But two months on, talks remain at an impasse.

On January 24, the Pentagon announced it has put about 8,500 troops on standby for possible deployment to eastern Europe.

Biden's national security adviser, Jake Sullivan, warned on Saturday that U.S. intelligence shows a Russian invasion of Ukraine could begin within days.

That came as NATO rebuffed Russian demands that included Ukraine be prohibited from joining the military alliance and that NATO pull back forces from Eastern Europe.

In a sign the U.S. is preparing for a worst-case scenario, the U.S. is evacuating most of its staff from the embassy in the Ukrainian capital of Kyiv and Americans are being urged to leave Ukraine.

On Saturday's Biden-Putin call, the U.S. president made a more forceful push to deter Putin from attacking Ukraine, the White House readout showed.

The U.S. remains committed to diplomacy to end the crisis, Biden said in Saturday's phone call, but is "equally prepared for other scenarios."

Both leaders will surely hope the next phone call prevents the world from having to find out what those scenarios are.