Democrats have a Joe Biden problem. The former VP might still lead the polls, but with serious concerns raised about his memory and mental state, nominating him to face Donald Trump in 2020 is a risk the party can’t afford.

Biden relayed a moving story of military heroism and his own role in honoring a US Navy captain to a rapt audience last week. The problem was, as the Washington Post reported, “almost every detail in the story appears to be incorrect.” In fact, Biden combined elements of three different events into “one story of bravery, compassion and regret that never happened.”

The generous interpretation here is that Biden did not intentionally lie, but genuinely mixed up the details due to failing memory. The cynical interpretation is that he embellished in order to play up his own role in the tale to win some campaign brownie points. Whatever the case may be, there’s no good way to spin it.

The Post’s report sparked a flurry of headlines and speculation about Biden’s mental state: “We Need to Talk about Joe Biden,” reads a National Review headline. “Joe Biden Needs An Intervention,” says Townhall. “Pull it together, Joe Biden,” argued an op-ed in the Post itself.

Everyone knows Biden has been a gaffe machine throughout his entire career, and Democrats have always considered his blunders to be part of a folksy charm. But it’s time to get real. As long as Biden leads in the polls, Trump will be laughing himself to sleep.

Just as they did in 2016 with Hillary Clinton – a centrist candidate with a troubling history who couldn’t excite young and progressive voters – the Democrats could very well be digging their own grave with Biden.

Trump has already begun to seize upon Biden’s increasingly frequent mistakes, dubbing him “sleepy Joe.” That’s in addition to “creepy Joe,” the other nickname bestowed upon the former VP due to his habit of showering unwanted physical attention onto women and girls. Following a recent slew of mistakes, Biden assured Democrats that he’s “not going nuts,” but is he?

Days before fabricating the military story, Biden appeared to forget Barack Obama’s name, stumbled, and called him “President… my boss” instead. Shortly before, he told reporters he was happy to be in Vermont during a campaign stop in New Hampshire. Twice since May, Biden has referred to Theresa May as “Margaret Thatcher.”

Earlier this month, he claimed Parkland school shooting survivors visited him when he was vice president, but he was not VP at that time. A career in politics at Biden’s level with busy schedules and events held all over the country no doubt lends itself to some confused dates and details, but these mixups indicate there could be something more going on.

Biden’s supporters might dismiss these concerns, but they would be the first to point to similar signs in Trump — confusion, forgetfulness, lying with regularity about big and small details, and so on — as proof that he is mentally unfit to lead the country.

Yet, even if 76-year-old Biden is experiencing memory loss, there could also be something more sinister at play. A recent New York Times piece recalling Biden’s calamitous 1988 run for president noted he was “prone to embellishment.” This is otherwise known as lying.

Over the years, Biden has lied about having marched in the civil rights movement. He has come under fire for plagiarism, more than once. He claimed falsely that he had been shot at in Iraq. Perhaps most disturbingly, Biden has even lied about the circumstances surrounding the tragic 1972 death of his wife and daughter, claiming falsely that Curtis Dunn, the driver who ran into their car was drunk. A police investigation found that the crash was not even Dunn’s fault. This particular lie of Biden’s is all the more malevolent when you consider that he waited for Dunn to die himself before libelling him as a drunk driver.

Is Joe Biden suffering worrying memory loss and cognitive decline, or is he just a liar? Recent and past evidence suggests it’s probably both, and the party will ignore these red flags at their peril.

Democrats already know Biden does not excite their base, and, more than a year away from the election, the media has begun talking about the Biden “enthusiasm gap.” That’s the very same phrase they used to describe how voters felt about Clinton three years ago.This is all aside from the former VP’s possibly failing memory and worrying propensity for embarrassing gaffes. If the Democrats are not careful, this could be like watching a replay of 2016.

It’s not as though the party does not have options. They are not perfect by a long shot, but a progressive like Bernie Sanders or a semi-progressive like Elizabeth Warren tick more boxes for young progressive voters who are becoming increasingly powerful within the party.

Biden is seen as the “safe” choice by many older, moderate Democrats, but so was Hillary Clinton. If there is one lesson they should have learned from that disastrous choice, it’s that centrist, establishment candidates are no match for a populist like Trump who can light a fire under voters.