Ronald Reagan was president and Michael Jackson’s song “Billie Jean” was at the top of the charts the last time Colorado held a special election for a vacant Congressional seat.

The year was 1983. Republican Jack Swigert, a former astronaut who served on the Apollo 13 mission, had won the general election the previous November, but then died of cancer just weeks later, before he could be sworn into office.

“When Jack died, of course, the election had already been held,” explained former Republican state party chair Dick Wadhams. “The process that ensued was off on its own.”

Now, more than 40 years later, Colorado is looking at another vacancy election, under very different circumstances.

Republican congressman Ken Buck’s announcement that he will leave his post earlier than expected has thrown a monkey wrench into what was already one of the state’s most hotly contested races this year.

There are currently nine Republicans actively running in the GOP primary race for Buck's seat in the next Congress. According to the Colorado Congressional Redistricting Committee, the fourth is Colorado’s most Republican district, with a nearly 30 point GOP advantage, so the winner of that primary race is expected to have a strong path to victory in November.

But with Buck stepping down from Congress next week, instead of next January, the state must now hold a separate election to fill the final months of his term.

That means the fourth district is on two parallel electoral tracks: the primary and then the general election to select a representative for the next Congress, and a special election this summer, with just one candidate per party and a winner who will serve for only the remainder of the year.

Wadhams said because these two separate processes are occurring at the same time, it makes everything more confusing.

“Somebody could win the special election to serve out the term in 2024, and somebody else could win the Republican nomination to run in the general election to serve a full two year term starting next year. That could happen,” said Wadhams.

It’s scheduled for June 25, 2024, the same day as Colorado's primary election.

State law required Gov. Jared Polis to set the date for the election between 85 to 100 days after the vacancy begins.

“Once the Governor sets the date, the parties will identify candidates, and unaffiliated candidates may petition onto the special election ballot,” states a letter from Polis’s office outlining the process.

In the vacancy election itself every registered voter in the district can vote.

The fourth congressional district is Colorado’s second largest, geographically. It spans 21 counties along the Eastern Plains and the I-25 suburbs. It’s the most conservative congressional seat in Colorado, with large swaths of farm and ranch land, but its most populated areas are Front Range suburbs in Douglas and Weld Counties.

Colorado rules allow one candidate per political party, picked by a special convention of party members from the district. Candidates who are already in the primary race can put themselves forward to be considered, but delegates at the convention could also go with someone who isn’t currently running and would serve out the year as essentially a placeholder in the office.

“It is possible we could have two different candidates running for CD4 at the same time,” Democratic Party Chair Shad Murib observed, noting that the whole situation becomes pretty complicated pretty quick.

“We will be convening a special convention no later than April 1,” said Murib. He said the gathering will include Democratic CO-04 central committee members, plus all local precinct organizers. Right now that list is around 215 people, but the number could increase.

Murib said, even though a final decision hasn’t been made, the convention will likely be held virtually; “I do think the virtual allows for a lot more participation.”

On the Republican side, a similar process will play out through that party’s CO-04 central committee, which includes state lawmakers, local GOP officials, the district's members on the state Board of Education and CU Board of Regents, and its current congressman, Ken Buck, among others.

Yes. In June, Republican, Democratic and unaffiliated voters will all receive ballots for the primary election. Additionally, all registered voters in the district will receive a separate ballot for the vacancy election.

“Everybody gets to vote in the special election,” said Wadhams. “In the primary only Republicans and unaffiliated voters can vote in the Republican primary and only Democrats and unaffiliateds can vote in the Democratic primary. So they really are two very different elections.”

Because the elections are happening on the same day, no candidate in the primary will have the power of incumbency. But Republican political consultant Ryan Lynch said he still thinks that if an existing GOP candidate is nominated for the vacancy, they'll have a strong advantage in the primary as well.

“What's the likelihood of whomever is on that special election ballot, is then also elected in the primary? I think it's pretty good,” said Lynch. He said voters who back the Republican candidate for the vacancy are more likely to vote for the same person if they’re also listed on the primary ballot.

For two different Republicans to win, “that would essentially mean people are voting for one Republican and against the same Republican on a different ballot at the same time,” said Lynch.

Candidates who are running in the primary race can put their names forward to be the candidate for the special election as well, but only one candidate from each party will be on both ballots.

To read more stories from Colorado Public Radio, visit www.cpr.org.