The red line the Mariners must not cross in Brendan Donovan trade talks

The Seattle Mariners still haven't responded to the loss of Jorge Polanco by bringing in an alternative bat. That's fine, given that it has only been a couple of days, but you do wonder if part of the hold-up is that potential trading partners are trying to force them to give into desperation.

Though we don't know if this is the case, we do know courtesy of Ken Rosenthal of The Athletic that the Mariners "remain in the mix" for Ketel Marte of the Arizona Diamondbacks and Brendan Donovan of the St. Louis Cardinals. The two present a case of "Better Player vs. Better Fit," with Marte in the first corner and Donovan in the second.

As noted by Rosenthal, this has a lot to do with the 28-year-old's defensive versatility. The Mariners also line up better as a trading partner for the Cardinals than they do for the Diamondbacks, who have a better chance of getting the pitching they desire from another team.

The red line the Mariners must not cross in Brendan Donovan trade talks

The Cardinals seem to merely want young talent to fuel a rebuild that is still in a nascent stage. The Mariners have lots of those, and we know from Katie Woo of The Athletic that the Cardinals have specifically inquired about switch-pitcher Jurrangelo Cijntje and slugging right fielder Lazaro Montes.

But what about…Colt Emerson?

Hey, don't look at us. Look at MLB Network insider Jon Morosi, who dropped Emerson's name on Monday in his weekly appearance on Wyman and Bob on Seattle Sports: "I don't see any way that [the Mariners] get Donovan without giving up one of the young infielders, either [Colt] Emerson, [Cole] Young or [Ben] Williamson. I think that you have to give up on of those players."

As speculative trade assets, two of those names are inoffensive. Williamson has Gold Glove-winning potential at third base, but the bat is in the shape of a question mark. And while Young was a top-100 prospect at the outset of 2025, his experience in the majors was mostly a reminder of how hard it is to go from "top prospect" to "productive major leaguer."

That same concern applies to Emerson, but with an asterisk that relates to how freaking talented he is. He has ascended to the No. 9 spot in MLB Pipeline's top 100, and the Mariners have not been subtle about wanting to give him a shot to earn the third base job in spring training. He otherwise doesn't have much left to prove in the minors after posting an .842 OPS and playing terrific defense across three levels this season.

To hand over a guy like that for Donovan truly would feel like a case of the Mariners giving into desperation. Donovan is solid, but it's hard to heap more glowing praise than that on a guy who's been a 2-ish WAR player in four MLB seasons. He's also 28 and only under club control through 2027, so it's not as if Seattle would be playing the long game in a trade for him.

In essence, an Emerson-for-Donovan swap would be the Mariners trading six years of a potential superstar for two years of a decent everyday player. They definitely need one of the latter, but the Cardinals insisting on getting the former should be cause to hang up and look elsewhere.