Rep. Fred Upton, the latest swing-district Republican to be the subject retirement rumors, is considering a Senate bid.

Factoring into the Michigan Republican's plans are whether he wants to run for re-election in what could be a midterm election made competitive by President Trump's low approval ratings.

But Republican operatives close to Upton insist that his interest in the Senate is legitimate and in an unofficial exploratory phase. Upton believes the GOP primary field is weak and that Democratic Sen. Debbie Stabenow is vulnerable.

Party insiders in Michigan said that Upton and his network of supporters in the state are fanning rumors that he might run for the Senate, as opposed to attempting to tamp them down.

"Fred is focused on doing his job but has heard from a great number of folks in Michigan who believe his abilities, vision, and natural focus on getting stuff done would serve our state well in the Senate," Upton spokesman Tom Wilbur told the Washington Examiner on Tuesday. "He continues to explore all of his options and is busy with a packed schedule both here at home and in D.C."

Trump won Upton's Sixth Congressional District by more than 8 percentage points, masking the historical competitiveness of this Southwestern Michigan seat.

Mitt Romney defeated President Barack Obama there by less than 2 points; it voted for Obama in 2008, twice for President George W. Bush and twice for President Bill Clinton. Upton has always had to work hard to keep his job.

That has fed retirement rumors, especially after other centrists and swing state Republicans, like Rep. Charlie Dent of Pennsylvania; Rep. Dave Reichert of Washington and Dave Trott of Michigan, called it quits, all in the last week, after eight months of dysfunction and a tumultuous summer with Trump in the White House.

Does Upton, 64, who had to give up the chairmanship of the House Energy and Commerce Committee because of party-enforced term limits, want to fight through political headwinds for the prize of another two years of diminished influence?

Some Republicans familiar with Upton's thinking say the answer is: not necessarily. Essentially, the answer might be "no," but that Upton also doesn't find the prospect of retiring appealing, either. Enter the Senate as the solution to Upton's dilemma.

"Everything I hear about Fred is that he's either going to run for re-election or he's going to run for the Senate, but that retirement isn't an option he's looking at right now," said a Republican operative from Macomb County, a suburban Detroit battleground.

Other Republicans who have followed Upton's career aren't so sure that he won't hang it up after more than 30 years in Congress. Republicans looking to succeed him are already lining up under that assumption. Still, these Republicans don't expect Upton to make a snap announcement.

Upton has periodically faced competitive primaries for his House seat, and his centrist record could put the GOP nomination for Senate out of reach. His lifetime score with the Club for Growth is just 54 percent. Heritage Action for America gave the congressman a score of 37 percent for 2015 and 2016.

"He needs a crowded and competitive four or five-way primary" to win the nomination, said a Republican operative with Michigan ties, who spoke on condition of anonymity to avoid publicly undercutting Upton. "He can get to 35 percent; not sure he can get to 40 percent. His base in Western Michigan is not in the heart of GOP land, but does give him a starting base."

Republicans fond of Upton are dismissive of this assumption, contending GOP base voters want results and pointing out that the congressman has worked well with Trump, advancing the president's agenda at every turn.

Robert Ritchie, a successful and famous musician who goes by the stage name Kid Rock, is the wild card in the Republican primary.

The Macomb County product, who still lives in town, has flirted with a Senate bid — or at least suggested that he's flirting with a Senate bid. If Ritchie ran he could swamp the GOP primary field much the same way Trump, another famous entertainer, overwhelmed the Republican presidential nominating contest in 2016.

Indeed, Trump was well received in Michigan. He won Upton's swing district easily and become the first Republican presidential candidate to win the state since 1988. That's why some Republicans are hoping Ritchie jumps into the race; they think he's the only way the GOP can defeat Stabenow in what could be a tough midterm.

In a Monday blog post, Ritchie alluded to his possible Senate run in a Trump-like rant excoriating his critics.

"My track record in Detroit and Michigan speaks for itself, and I would dare anyone talking trash to put theirs up against mine. I am also a homeowner and taxpayer in the city of Detroit, so suck on that too!" he said.