The opinions expressed below are Jon Keller's, not those of WBZ-TV, CBS News or Paramount, a Skydance Corporation.  

Longtime incumbent Republican Maine Senator Susan Collins has a new challenger: the state's Democratic Governor Janet Mills.

Governor Janet Mills has announced her intention to run in next year's midterm election. But there's a twist to Mills' candidacy that highlights the backlash against aging politicians.

Remember last winter when the 78-year-old governor clashed with our 79-year-old president over banning transgender athletes? 

"You better do it because you're not going to get any federal funding if you don't," Donald Trump warned Mills during a White House event with governors. 

"I'll see you in court," replied Mills, and her announcement video triumphantly recounts the incident and concludes, "I did see him in court, and we won!"

That is the centerpiece of Mills' run for Senate, which comes with an unusual promise: She told The Boston Globe she will only serve one six-year term, a pledge that inserts her into the debate over whether or not 79-year-old Massachusetts Senator Ed Markey should be seeking another term next year, itself an offshoot of fallout from octogenarian Joe Biden's ill-fated re-election bid.

"We stood up to Trump and stopped him from cutting the school lunch program for Maine kids. But there are too many politicians in Washington, including Susan Collins ... who've forgotten their principles and let bullies like Trump have their way," said Mills in her campaign video. And if Mills wins her party's nomination to go against five-term incumbent Collins, it promises to be an issue that Collins signed a pledge to serve just two terms when she was first elected in 1996.

"There's a lot of good people out there that can step up and take a turn," said Aaron Dukett, of New Hampshire, regional director for U.S. Term Limits, which promoted the term limits pledge and lobbies for bringing "some fresh perspective and fresh ideas to modern 2025 problems and not bringing a 1985 mindset to them."

Mills' video concludes, "This election will be a simple choice. Is Maine gonna bow down or stand up? I know my answer." But before she can take on Collins, she'll have to beat several candidates in the Democratic primary, including the likes of oyster farmer Graham Platner, who is nearly 40 years younger than Mills.

So, you wonder if her surprise pledge to serve just one term is an early move to pre-empt the age issue in the primary race. If so, that would be just the latest example of how that issue is emerging as a potent one in the 2026 elections, at least on the Democratic side.