Michigan Sen. Debbie Stabenow speaks during a news conference at the US Capitol in Washington, DC, on December 6, 2022.
CNN  — 

Longtime Michigan Sen. Debbie Stabenow is calling it quits and will not stand for reelection in 2024.

At a minimum, her decision makes Democrats’ already difficult job of retaining Senate control in 2024 even harder. Senators caucusing with the party hold 23 of the 34 seats expected to be up for reelection. Seven of them represent states Trump won at least once. This includes Michigan.

Sen. Gary Peters – the last Democrat not named Stabenow to run for Senate in Michigan – won reelection by less than 2 points in 2020.

Stabenow likely would have made Democrats’ job easier had she opted to run again. After narrowly unseating Republican Sen. Spencer Abraham in 2000, she has won reelection by at least 5 points in three subsequent contests.

But Democrats now have a battle on the horizon in another state that flipped from Donald Trump in 2016 to Joe Biden four years later. Beyond Michigan, Democrats face a messy situation in Arizona with Sen. Kyrsten Sinema becoming an independent.

With 51 senators now caucusing with Democrats, losses in Arizona and Michigan alone could be enough to flip the chamber to Republicans.

Yet, Republicans’ ability to flip Michigan will be highly dependent on two important questions.

First, what type of party do GOP primary voters want?

And second, will Republicans in key Great Lakes battleground states continue to outperform national results if Trump isn’t on the ballot?

In 2022, we saw GOP primary voters across the map select nominees who ended up being rejected by the general election electorate. Republicans underperformed the partisan fundamentals in a number of key Senate races, allowing Democrats to maintain control of the chamber while narrowly losing the House.

There were several examples of this in Michigan last year. While there was no Senate race, the state held elections for key statewide offices, including governor, attorney general and secretary of state. The Republican candidates for these positions promoted false claims that Biden had not won the 2020 election legitimately.

The result was that none of them came close to winning any of these races. This was most evident in the gubernatorial contest, where Democratic Gov. Gretchen Whitmer turned what should have been a close race against Republican Tudor Dixon into a double-digit blowout.

If Republicans are going to want to compete in Michigan in 2024 – or any swing-state Senate races in two years – primary voters will likely need to choose more mainstream candidates than they did in 2022.

Of course, it won’t just be about individual candidates. It will be about regional trends as well.

One of the biggest electoral changes in the past decade has been the Republican breakthrough in Great Lakes states such as Michigan, Pennsylvania and Wisconsin. They went from voting to the left of the nation in the 2012 presidential election to voting to the nation’s right in 2016 and 2020. This was in large part because of Trump’s appeal to White voters without a college degree.

But Trump may not be on the ballot in 2024, and it’s unclear whether the pro-Republican trend in these Great Lakes states will continue without him.

Look at what happened last year. Michigan voted to the left of the nation in US House races. Pennsylvania and Wisconsin voted basically in line with the nation, once you account for uncontested races.

Indeed, it would not be surprising to see a shift in how states vote relative to the nation if Trump is out of the picture. This has happened every eight years in recent cycles (e.g., 1976, 1984, 1992, 2000, 2008 and 2016).

And that would make Democrats less vulnerable in Michigan than you might think, even without Stabenow as their nominee. Keep in mind that Democrats haven’t lost a Senate race in the Wolverine State since 1994.

A return to the pre-Trump era in Michigan and other key Great Lakes states may also mean that the advantage Republicans have held in the Electoral College relative to the popular vote in the two most recent presidential elections may not materialize in 2024.

That’s something Democrats would certainly welcome going into 2024 after one of the closest midterm cycles of the past century.