Washington Governor and 2020 presidential candidate Jay Inslee is upping the pressure on the Democratic National Committee to hold a debate exclusively devoted to climate change, with a letter to Chairman Tom Perez.

“Last week, the Democratic National Committee announced further details for the third and fourth Democratic primary debates, including dates, media partners, and new participant qualification rules,” Inslee wrote, according to a draft seen by The Daily Beast. “On one crucial detail, the DNC was completely silent—whether it would listen to the tens of thousands of Democratic activists who are demanding a debate solely focused on the defining issue of our time—the climate crisis.”

In April, Inslee created a petition to put pressure on the DNC to host a climate debate, which was supported by a number of the other presidential candidates in the race. A number of other groups, including Sunrise Movement and the U.S. Youth Climate Strike Team have similarly urged the committee to focus on the issue, which got woeful attention in the last Democratic presidential primary and has become one of the most crucial to voters this cycle.

“As Democrats, we must do better in 2020,” Inslee writes in the letter, referring to the lack of climate-change questions in general-election debates in 2016. “On behalf of grassroots Democrats and environmentalists around the country, I’m asking the DNC to lead the way and announce a climate debate today.”

Inslee suggests that one of the first four scheduled debates already on the books be specifically about climate change and asked for a response from Perez by June 12.

According to a source familiar with the situation, Inslee also called Perez last Friday and the chairman made no commitment.

“The Democratic Party’s response to climate change cannot only be a few quick questions in the first debates where, in 60 seconds, candidates merely agree that this issue is important, and move on,” he writes. “We need a full debate to really wrestle with who has the best plans to defeat this existential crisis, who has demonstrated the commitment it will take to get this job done, and who understands the scale of ambition necessary to see this mission through to completion.”