The Colorado Democratic Party on Friday scheduled an online convention for April 1 in the state’s 4th Congressional District to nominate a candidate to replace Republican U.S. Rep. Ken Buck, who announced his resignation this week.

The Democrat chosen at the convention will run against the Republican nominee — and any third-party or unaffiliated candidates who qualify for the ballot — in a special election on June 25, the same day as the state’s primary election.

Buck said on Tuesday that his last day as a member of Congress will be March 22, creating a rare House vacancy that must be filled in a special election — only the second in state history.

The Colorado GOP has yet to release the procedure it’s chosen for picking a nominee, which must be accomplished by April 1 under state law.

Noting that Democrats had little guidance on how to nominate a candidate beyond a requirement to assemble a “convention of delegates,” state party chair Shad Murib said he decided to model the process on the party’s method for filling vacancies in other partisan elected offices.

According to an outline of the Democrats’ convention rules, convention delegates will include members of the 4th CD’s central committee — made up of county party officers and elected officials — and precinct officers who live in the district, which covers Douglas County, a small portion of Larimer County and the Eastern Plains.

“I care about fairness, I care about transparency, and I care about making sure every candidate has the same access to resources through the party and statutes and everyone else,” Murib said. “And so we’ve decided to make this process look very familiar.” Murib added that he wanted to “expand it as far as I can, because I don’t want it to be a small group, I want it to be as large as it is.”

A party spokeswoman said Friday that roughly 275 delegates will be eligible to vote at the convention, which is scheduled to start at 5:30 p.m. on the Zoom platform. The meeting will be simulcast on the Democrats’ YouTube channel, Karin Asensio, the Democrats’ executive director, added.

Asensio told Colorado Politics on Friday that the same four Democratic candidates who have been running in the primary had notified the party they intend to seek the nomination for the special election. They include Isaac McCorkle, who lost the 2020 and 2022 elections to Buck; former U.S. Senate hopeful Karen Breslin; and first-time candidates John Padora and Trisha Calvarese.

The nominee to replace Buck must be chosen by a majority vote of delegates. If no candidate wins on the first round of balloting, the lowest-polling candidate drops out before the next round, and so on until a candidate receives a majority.

The potential nominees are slated to take part in a 40-minute candidate forum before the formal meeting gavels in at 6:40 p.m., the Democrats said.

While the 4th CD ranks as the most favorable toward Republicans in the state, the district’s Democratic chair said her party isn’t conceding either upcoming election.

“For too long, Ken Buck and the Republican Party have catered more to what the Washington D.C. power brokers want, all while leaving our farmers, ranchers and teachers behind and voiceless,” said Lisa Chollet, in a statement. “We look forward to giving voters a real choice not just in this special election but also in November.”

The most prominent Republican candidate for the seat, U.S. Rep. Lauren Boebert — who moved across the state in January to run in Buck’s district after he announced he wouldn’t seek reelection — said Wednesday she won’t seek the GOP nomination for the special election and plans to instead focus on winning the primary.

Other Republicans already running in the primary have said they hope to win their party’s nod for the special election, including former state Sens. Jerry Sonnenberg and Ted Harvey, state Rep. Richard Holtorf and nonprofit founder Deborah Flora. Another primary candidate, state Rep. Mike Lynch, told Colorado Politics this week that he hadn’t decided whether to pursue the nomination for the special election.