In May, Reuters news agency first revealed that Democratic presidential candidate Joe Biden is crafting a “middle ground” climate policy.

In a crowded field of Democrats, some of them progressive and committed to aggressively combating climate change, Biden’s policy proposal stood out like a relic from the Obama era — a milquetoast, Republican-like compromise.

As Business Insider reported, soon after news about Biden’s climate plan broke, activists, progressive groups, and other candidates blasted the former vice president’s plan for not going far enough, contrasting it with the ambitious Green New Deal.

In late May, the famous environmental organization Greenpeace gave Biden a “D-” grade, ranking him near the bottom of the Democratic field.

The words “middle ground” have since been launched at Biden by journalists, activists, political opponents, and Democratic hopefuls looking to beat him in what is starting to look like a volatile, exciting primary race.

As the polar opposite of Biden, and the most progressive candidate in the race, Independent Vermont Senator Bernie Sanders has often used the words “middle ground” to question Biden’s past and overall approach to politics, frequently without even mentioning the former vice president by name.

Sanders did the same on Sunday during the Iowa Democratic Party Hall of Fame forum, The Washington Examiner reports.

Without referring to Biden by name, the Vermont senator blasted the former vice president’s “failed” political strategy, suggesting that nominating Biden could lead to President Donald Trump winning in 2020.

“Now I understand there are well-intentioned candidates who believe the best way forward is a middle ground strategy that antagonizes no one, that stands up to nobody, and that changes nothing. In my view, that approach is not just bad policy, but it is a failed political strategy that I fear could end up with the reelection of Donald Trump.”

To illustrate what the opposite of a “middle ground” approach to politics is, Sanders discussed his signature issue: healthcare.

Sanders railed against “the power of the insurance industry,” and “the greed of the pharmaceutical industry,” making the case for universal, single-payer healthcare, which Joe Biden opposes.

“The American people want change, they want real change, and we have got to provide that change,” he said.

Bernie Sanders leads a solidarity march through Cedar Rapids ahead of today’s Iowa Hall of Fame dinner. pic.twitter.com/GYXAK7AxTR — Eric Bradner (@ericbradner) June 9, 2019

Sanders has issued similar warnings on many occasions, most recently warning in another thinly-veiled shot at Biden that a “status quo” candidate would not be able to defeat Trump.

As The Inquisitr reported, Sanders also argued that the Democratic Party needs to hold Trump accountable and push its own agenda at the same time, instead of allowing the commander-in-chief to consume all of its energy.

Joe Biden is leading the crowded Democratic presidential field in Iowa, with Elizabeth Warren and Bernie Sanders in a tight secondary grouping according to a new pollhttps://t.co/QiuIy7zNVF — POLITICO (@politico) June 9, 2019

Despite backlash, Biden has maintained a strong lead in the polls, and remains the Democratic front-runner with a double-digit lead over Sanders.