Former U.S. Vice President Joseph Biden, once the front-runner in the 2020 Democratic presidential race, has seen his candidacy fall upon hard times in recent months. This is at least in part due to the wave of negative media mentions that Biden received in the wake of demonstrably false accusations from U.S. President Donald Trump of improper activity by Biden in Ukraine when he was leading the Obama administration’s policy toward Kyiv.

Biden suffered a four-place finish in the opening nominating contest on Feb. 3 in Iowa, a caucus state that enables the professional activist class which supports new front-runner Bernie Sanders. Sanders, an avowed leftist-socialist from Vermont who has refused to join the Democratic Party, then exploited his home-court advantage in the neighboring state of New Hampshire to take the second nominating contest as well, leaving Biden reeling and opening the door for several other candidates to claim the mantle of Sanders’ main challenger. A third win on Feb. 22 in Nevada, another small caucus state, cemented Sanders’ status.

Billionaire Michael Bloomberg, one of the world’s richest men, leaped into the race this winter amid the signs of Biden’s difficulties, presenting himself as a savior for the moderate wing of the party against Sanders, who many political analysts of various persuasions believe would be a long-shot to defeat to Trump in November.

But Bloomberg was ill-prepared and unprofessional in the Democratic debate on Feb. 19, blunting the momentum that his advertising campaign of hundreds of millions of dollars had created for him and creating the impression that what Democrats really need is Bloomberg’s money, not his candidacy.

Bloomberg ostensibly entered the race to stop Sanders but instead has actually been helping him by diluting the vote of the non-Sanders candidates, and of Biden first of all.

At this critical juncture of the race, with Bloomberg floundering, Biden appears to be the only candidate still capable of putting together a coalition to prevent Sanders from quickly running away with the Democratic nomination in the upcoming March primaries.

It is clearly understood by virtually all Americans working in Ukraine that Biden was doing his job of advancing U.S. policy goals, and doing it well, when he forced then-President Petro Poroshenko to fire General Prosecutor Victor Shokin in March 2016 by threatening to withhold U.S. taxpayer-funded assistance from Kyiv. Even if Shokin was not corrupt himself, he surely presided over an office in which state prosecutors demanded and received large sums of cash in return for opening and closing criminal cases.

What has received comparatively little attention is that in forcing Shokin’s removal as general prosecutor, Biden was actually making it more likely, not less, that Ukraine would investigate the activity of natural gas company Burisma, where Biden’s son Hunter was a highly-paid board member. Shokin, despite his recent claims to the contrary made to partisan pro-Trump US media outlets, had clearly slow-walked the existing fraud investigation into Burisma during his tenure at the GPO in 2015 and early 2016.

There is an obvious reason why Trump was so obsessed with Biden that he insisted on calling up Volodymir Zelenski to ask the Ukrainian leader for the special favor of opening a publicized criminal investigation into Biden’s role in Kyiv. Trump saw – and likely still sees – Biden as his only potential opponent who is capable of attracting a wide swath of non-ideological voters in the center of the US electorate without losing too many left-leaning voters.

Trump has even taken to applauding and encouraging Sanders on his Twitter account in recent days, amid news that US intelligence agencies have determined that the Kremlin is working to aid the Sanders campaign in hopes that he will take the Democratic nomination and then lose to Trump in November. This creates the uncomfortable impression that Trump, Sanders, and Russian President Putin are all playing on the same team against the Democratic Party.

Although Sanders currently polls fairly well (about the same as Biden) in a head-to-head matchup against Trump, demonstrating a small lead, it should be remembered that Biden is already battle-tested, having been under an onslaught of Trump and Republican attacks for more than a year. On the other hand, Sanders has suffered barely a scratch from the vaunted GOP attack machine, as he has not yet been targeted.

Biden has always been the strongest 2020 candidate for those who understand how serious the threat is that Trump presents to the U.S. constitutional order. After the failed impeachment attempt by Democrats, Trump feels more enabled than ever to dismantle the US justice system and to politicize the security agencies that protect the country from foreign attacks. Trump will find no pushback from Sanders on this, as Sanders and his hardcore supporters seem to believe that US security agencies are themselves the root of most of the world’s evil.

Indeed, Sanders’ foreign policy perspective is strikingly similar to that of the minor leftist candidate Tulsi Gabbard, who has been a favorite of the Russian troll universe for several years thanks to her enthusiastic promotion of hands-off isolationism.

Allowing Sanders to become the Democratic nominee for president without thoroughly vetting and challenging the Sanders-Gabbard foreign policy worldview would be a dereliction of duty and an inexcusable capitulation to Donald Trump’s re-election. Democrats who argue that digging too deep into Sanders’ past risks weakening him in the general election should realize that, although Democrats might be reluctant to confront Sanders on foreign policy, including his support for totalitarian leftist regimes, the Trump campaign will not fail to do so.

Biden may not end up defeating Sanders, but he is surely the best-placed candidate to ensure that Sanders does not continue to get a free ride through the primary process. Biden has been a friend to Ukraine, and to the Americans who have worked here to try to help the country realize its potential, for more than two decades. His bid for the presidency deserves our support in this decisive hour.