Former top Trump Russia adviser details the sharp contrast between the former President and Biden

Fiona Hill doesn't know whether President Joe Biden can lead Western allies to ward off Russia's threat to Ukraine. But unlike his predecessor, he's trying.

Hill has a special vantage point on this slow-rolling crisis that US officials say could bring war in Europe at any moment. As a White House national security aide, she advised then-President Donald Trump on Russia and Ukraine -- and became a star witness in impeachment proceedings that resulted from his conduct.

Now, outside the government as a Brookings Institution senior fellow, she's among the Russia specialists Biden has consulted as he revives foreign policy priorities shared by every president since World War II except Trump.

After Trump derided and weakened the North Atlantic Treaty Organization, Biden has rallied NATO on Ukraine's behalf.

After Trump pressured Russia's beleaguered neighbor for his personal benefit, Biden has steeled Americans for shared sacrifice in defense of Ukraine's right of self-determination.

After Trump deferred to Russian President Vladimir Putin over the US government's own intelligence agencies, Biden has deployed those agencies' tradecraft in a multi-pronged transatlantic effort to deter Russian aggression.

"You couldn't get a sharper contrast," Hill observed in an interview.

For the moment, at least, she sees Biden's approach paying some dividends.

As described in her recent memoir, There Is Nothing For You Here, Hill followed an unusual path to becoming one of America's leading experts on Russia. Raised in a working-class family in Britain, she parlayed academic scholarships into advanced degrees from Harvard and an analyst's job at the National Intelligence Council beginning in 2006 during President George W. Bush's administration.

Witnessing Britain's industrial decline helped her understand the populist appeals Trump rode to the White House. But the celebrity real-estate developer's handling of foreign policy in the Oval Office -- driven not by expertise or the national interest but by his personal experiences, impulses and interests -- was like nothing Hill or her national security colleagues had ever seen.

"There's no Team America for Trump," Hill recalled. "Not once did I see him do anything to put America first. Not once. Not for a single second."

It showed in Trump's praise for the authoritarian leader of Russia, an American adversary that had boosted his finances as a business executive. It showed in his reluctance to embrace America's mutual defense commitments to European allies, which for decades have constrained Russian behavior; instead, Trump treated NATO as what Hill called a "protection racket."

Most notoriously, it showed in Trump's attempt to squeeze Ukraine's President for manufactured dirt on Biden to help his 2020 election campaign. He held up American military aid as a political lever as Ukraine faced the long-running Russian military threat that now has the entire world on edge.

"All this did was say to Russia that Ukraine was a playground," Hill said.

At home, Trump softened Republicans' once-hawkish approach to Russia. Today, the leading Fox News hosts and other conservative voices -- "the ultimate stooges," as Hill calls them -- buttress Russian arguments as armed conflict looms.

Yet even friendly foreign counterparts found limitations in Trump's scattershot style, which for Hill evokes the old saw about "playing chess with a pigeon." Russia's bid to upend the post-Cold War security order in Europe, beginning in 2008 with its invasion of Georgia and continuing with its 2014 seizure of Crimea -- requires a steadier negotiating partner.

"Ultimately Putin wants some kind of deal," Hill said. "They think Biden is the kind of president who could actually make a deal. Trump never could."

So far, Biden has held NATO allies together in rejecting Russia's core demands, bolstering their forces in Europe and threatening punishing sanctions even though they guarantee domestic economic blowback. Steeped in decades of bipartisan foreign policy consensus, the Democratic President has also drawn support from top Republicans such as Senate Minority Leader Mitch McConnell who have shunned Trump's embrace of Putin.

That demonstration of resolve has at minimum made Putin stop and think. Biden has warned for weeks that Russia could launch a new invasion of Ukraine at any time. It hasn't yet.

"They might have thought we were going to crumble, and we didn't," said Hill, who became an American citizen twenty years ago. "It might have deterred a full-scale invasion. Now (Putin) is basically recalibrating, recalculating."

But durable success for Biden and European allies will depend on staying power. Even if Russian tanks don't roll across the border, Hill envisions an extended "boa constrictor" siege in which Putin applies escalating pressure in hopes of bending Ukraine to Russia's will.

"The real challenge is keeping everyone together for a considerable period," Hill concluded. "It's going to go on a long time."