“This is no time to take a risk. We need our strongest candidate. So let’s nominate the Democrat Trump fears the most.”

That was Joe Biden’s message in an ad released in January ahead of the Iowa caucuses, and it is an electability argument that Biden has made central to his White House bid.

But, as voters in six states headed to the polls Tuesday, progressives and supporters of Sen. Bernie Sanders (I-Vt.) argued that nominating the former vice president would be a massive risk for the Democratic Party, given Biden’s voting record and current policy positions.

“You know, I keep hearing this thing about Joe Biden being ‘a safe candidate.’ Safe for who?” asked environmentalist and author Naomi Klein, who endorsed Sanders for president, said in a video released Monday. “I know he goes to corporate fundraisers and tells people that nothing’s going to change. So he’s clearly telling them that he’s a safe candidate for them. What’s safe for the ultra-rich is incredibly dangerous for everybody else.”

Klein added that Sanders’ support for Medicare for All, a Green New Deal, and other transformational policies make the Vermont senator the most electable 2020 Democrat.

“Policies that don’t challenge the status quo right now are incredibly dangerous,” said Klein. “Bernie Sanders is the only candidate whose policies are bold enough to actually keep us safe… Bernie Sanders is not a risky candidate against Donald Trump. He is, in fact, the safest candidate.”

“Joe Biden is not safe. Not safe for the planet. Not safe for our health. Not safe to run against Trump,” Klein tweeted.

Current Affairs editor Nathan Robinson, an outspoken Sanders supporter, wrote Saturday that a Biden nomination could represent a repeat of 2016, which saw the supposedly safe establishment candidate Hillary Clinton lose to reality television star Donald Trump.

Robinson accurately predicted in a February 2016 article that Clinton would lose to Trump in a head-to-head matchup and made the case for Sanders as the more electable candidate.

On Saturday, Robinson echoed that case, pointing to Biden’s past support for Social Security cuts, votes in favor of the 1994 North American Free Trade Agreement (NAFTA) and 2003 invasion of, and other elements of his record.

“It is Biden, not Sanders, who would be the risky bet,” Robinson wrote. “A Sanders presidency is nothing to fear, but a Biden nomination certainly is.”

Biden is leading Sanders by just under 100 delegates—670 to 574—heading in to Tuesday’s primaries in Idaho, Michigan, Mississippi, Missouri, North Dakota, and Washington. A total of 365 pledged delegates are up for grabs Tuesday, and 1,991 delegates are needed to secure the nomination on the first ballot.

“Bernie Sanders is the safe choice,” pro-Sanders group People for Bernie tweeted Tuesday. “Today is the day to #VoteForBernie.”

Jeet Heer, national affairs correspondent for The Nation, argued in a column Monday that nominating Biden is a risk not only because of his potential vulnerabilities in a general election matchup with Trump, but also because of how the former vice president has promised to govern should he win the presidency.

“Given already low interest rates, a stalling global economy, and the need for new infrastructure (both for its own sake and also to prepare for climate change), this is the ideal time for a president who isn’t afraid to argue for big structural changes and to go full Keynesian,” Heer wrote. “But that’s exactly the president that Joe Biden would not be. He’s running to be a business-as-usual president. Given the real problems facing the world, that’s a dangerous risk.”