Ever since Illinois voters gained the right to directly elect their U.S. senators in 1913, they have largely embraced — whether by choice or chance — an unofficial tradition of splitting the state’s two Senate seats geographically with one coming from the Chicago area and the other from downstate, regardless of party.

For the past 28 years, it has been Democratic Sen. Dick Durbin of Springfield who has served as the downstate senator alongside a string of Chicago-area counterparts: Democrat Carol Moseley Braun of Chicago, Republican Sen. Peter Fitzgerald of Inverness, Democratic senator and future President Barack Obama of Chicago, appointed Democratic Sen. Roland Burris of Chicago, Republican Sen. Mark Kirk of Highland Park and current Democratic Sen. Tammy Duckworth of northwest suburban Hoffman Estates.

But with Durbin’s announcement Wednesday that he will retire following the 2026 election, the issue of geographic balance of Illinois’ Senate representation appears to be at serious risk of coming to an end, at least based on the candidates that so far have shown interest in succeeding him. If that remains the case, it could further the cultural, political and ideological divide between upstate and downstate Illinois.

“I’m very concerned about that,” said Robin Johnson, a governmental relations, public policy and political consultant who also is an adjunct professor of political science at Monmouth College in far west-central Illinois.

“Durbin’s staff was very responsive and understood the needs of downstate Illinois. That’s important, that you didn’t have to explain things to them. They understood,” he said. “And I just worry, and I think a lot of people are, based on the conversations I’m having, worried that we’re going to lose that.”

A day after announcing he would retire at the end of his term, Durbin acknowledged to reporters outside his Springfield home that as a downstate Democrat, he was “kind of a vanishing breed,” a reflection of the political evolution of the region that has grown staunchly Republican due in part to the loss of union coal mine and manufacturing jobs over the decades.

“My message to everyone interested in running for office statewide: Run in the entire state from one corner to the next. Don’t assume a damn thing. These are voters who want to hear from you and want to know if you’re going to make their lives any better,” the 80-year-old senator said.

Saying he was not concerned about downstate getting shortchanged by a Chicago-area successor, Durbin said, “I think the person who is successful in running for this office is going to understand that they’ve got to not only represent the entire state, they’ve got to work the entire state.”

Among the list of Democratic contenders interested in Durbin’s seat are Lt. Gov Juliana Stratton of Chicago, who has formally announced her candidacy, U.S. Reps. Raja Krishnamoorthi of Schaumburg, Robin Kelly of Matteson, Lauren Underwood of Naperville and state Treasurer Michael Frerichs of Chicago.

Some have downstate connections. Stratton’s office leads the governor’s Rural Affairs Council. The five-term Krishnamoorthi was raised in Peoria. Kelly, in her 12th year in Congress, got her bachelor’s and master’s degree at Bradley University in Peoria and her congressional district stretches from Chicago to Danville. Frerichs, who held Champaign County office before being elected to the legislature and then three terms as treasurer, had lived in Champaign until moving to Chicago not long ago.

“They’ve all got little boxes they can check,” Johnson said. “The bottom line is going to be, how well do they really understand the needs down here and come down and be able to really understand it, other than just checking a box.”

Though he did not announce his candidacy last week, Krishnamoorthi appeared Thursday at a wholesale food distributor in Chicago’s New City neighborhood where he addressed the geographic tradition by touting his downstate personal history.

“I think that we need a senator for sure who is going to fight for every region of the state. I happen to be from Peoria, I’m a son of downstate, so I have deep roots and ties to Peoria and central Illinois and downstate Illinois,” he said. “I think that it’s important that we, at the same time, deal with the issues that affect the Chicago area, that we remember that the rest of the state needs an essential voice wherever the person, he or she, is fighting for their values.”

Republican U.S. Rep. Darin LaHood of Peoria, who has served 10 years in the House, has acknowledged considering a Senate bid and would be a bona fide downstate candidate.

But there are questions about whether LaHood would give up a solid GOP congressional seat and how an ally of President Donald Trump would fare in the increasingly Democratic and vote-rich Chicago area, concerns amplified in an off-presidential year election that normally favors out-of-power candidates.

Illinois’ history is replete with examples of the downstate-upstate Senate split. In the 1940s, there was powerful downstate Democratic Sen. Scott Lucas from Mason County, who served with Chicago Republican C. Wayland Brooks and Democrat James Slattery. In the 1950s and 1960s, there was liberal University of Chicago economist Paul Douglas and Senate Republican leader Everett McKinley Dirksen of Pekin.

Douglas’ successor, Republican Sen. Charles Percy of Kenilworth, served with Democratic Sen. Alan J. Dixon of Belleville in the early 1980s. Percy’s successor, Democratic Sen. Paul Simon of Makanda in southern Illinois, served with Dixon and then Moseley Braun in the early to mid-1990s.

John Jackson, visiting professor at the Paul Simon Public Policy Institute at Southern Illinois University, said he thought it was “highly likely” the next senator would come from the Chicago area. But he also said it pointed to how politically polarized the state has become.

“While the Democrats do extremely well statewide, it is also extremely narrow in its geographical base that they’re able to do that well. And of course, northeastern Illinois is the key to that,” Jackson said of the vast political split between the Chicago metropolitan area and the rest of the state. Jackson also said the upstate-downstate splitting of Senate seats was more representative of a time when “downstate was a bigger part of the equation” in statewide elections.

Durbin, who succeeded Simon after the senator’s retirement in 1997, was successful as a downstate politician in embracing the entirety of Illinois and its needs. He helped deliver billions of dollars in federal assistance, ranging from O’Hare International Airport to a massive rail relocation project in Springfield as well as helping to deliver grants to health care initiatives in both the city and rural areas.

“Dick Durbin has an office in the Paul Simon federal office building in downtown Carbondale, and he has had it the whole time, and that symbolic presence is worth a lot,” Jackson said.

“Just be sensitive to those things and help downstate Democrats not get shut out,” he said in offering a downstate strategy for the potential Democratic Senate candidates. “It seems to me, and it is clear to anyone, we’re one big state. We’re not going to let anybody secede. And so let’s start talking about things that unify us.”

Johnson said the candidates will have to “put together a message based on what’s really going on down here, and understand people’s lives as they exist and not as what pundits, consultants say they do through polls and social media. It’s coming down here and spending some time.”

But can the state’s geographic political divide be bridged?

“You’re one good leader away from making it happen, somebody that can speak to how the state is really tied together, our fortunes are tied together, and we don’t get there by threatening to secede and go to Indiana or Iowa,” Johnson said. “We get there by taking an honest appraisal of what interests we’ve got in common. And I think that’s the challenge before candidates running for the Senate from both parties.”

Chicago Tribune’s Jeremy Gorner in Springfield and A.D. Quig in Chicago contributed.