SAN FRANCISCO ― Sen. Bernie Sanders (I-Vt.) took a veiled shot at former Vice President Joe Biden on Sunday, arguing in a speech to the California Democratic Party convention that Biden’s “middle ground” approach would fail both to address the country’s problems and to unseat President Donald Trump.

Sanders, the second-to-last presidential candidate to speak at the convention, did not mention Biden by name.

But his refrain about the perils of “middle ground” policies was a clear reference to Biden energy adviser Heather Zichal’s suggestion in May that Biden would pursue a “middle ground” on climate policy.

“We have got to make it clear that when the future of the planet is at stake, there is no ‘middle ground,’” Sanders declared. “We will take on the fossil fuel industry and transform our energy system.”

He went on to say that there was likewise no “middle ground” on curbing corporate power, abortion rights, health care, gun control, prescription drugs or foreign policy.

Sanders also made the case that running as a candidate seeking merely to restore the pre-Trump status quo, as Biden sometimes suggests, would not be enough to prevail in a general election.

“In my view, we will not defeat Donald Trump unless we bring excitement and energy into the campaign, and unless we give millions of working people and young people a reason to vote, and a reason to believe that politics is relevant to their lives,” he said. “We cannot go back to the old ways, we have got to go forward with a new and progressive agenda.”

Sanders’ comments echoed remarks by some of his fellow Democratic presidential candidates, Sen. Elizabeth Warren of Massachusetts, South Bend, Indiana, Mayor Pete Buttigieg and Rep. Eric Swalwell of California. All three contenders took subtle swipes at Biden’s bipartisanship-focused candidacy in their remarks to the convention on Saturday.

The broadsides against Biden were particularly notable because Biden was not there to defend himself. Rather than attend the party convention, where liberal activists hold outsize sway, Biden spoke at a Human Rights Campaign dinner in Columbus, Ohio.

Sanders, who consistently comes in second behind Biden in primary polls, is mounting a serious bid to win in California. He announced a series of senior staff hires ahead of the weekend’s events, courted Democratic activists at several of the California Democratic Party’s breakout caucuses and held rallies in Pasadena and San José over the weekend.

The Golden State primary, which is open to independents, is due to take place on Super Tuesday, March 3. The early timing of the contest gives the state greater influence over the Democratic primary than it had in 2016, when its voting was held in June.