Massachusetts Governor Charlie Baker has enjoyed bulletproof approval ratings for the last six years. But a new Republican-focused poll shows what could be some cracks in his support, at least among his own party. GBH Morning Edition host Joe Mathieu spoke with GBH News State House reporter Mike Deehan about the poll results and what they could mean for Baker in a potential 2022 reelection campaign. The transcript below has been edited for clarity.

Joe Mathieu: So this latest [poll] came out just a week ago. The last big poll we talked about here on Morning Edition, [there was] 74 percent support for Baker. Governors [and] politicians of any kind would cut off their arm for a number like that. But this newer poll out yesterday isn't quite so positive. How come it's got your attention?

Mike Deehan: It's from the Mass Fiscal Alliance and some other New England operations that are really conservative-focused. They're not fans of Baker, but that shouldn't discount their findings. Anyway, the takeaway here is clear on what this poll found. Baker could have trouble in his own primary if he does decide to run for a third term. That's because it seems like Republican voters care more about the vaccine rollout. He's getting high marks for the business reopenings from conservatives and from the general public, but the vaccine rollout doesn't seem to be all that great, as far as reflecting on Baker.

WATCH: Poll shows most disapprove of Baker's vaccine rollout plan.

Mathieu: Of course, we could have a lot of evolution in the vaccine story. You add Johnson & Johnson, maybe this whole timeline gets moved up and he looks like a hero, Mike. But if he does not run again, who could step into the race? Are there any real candidates?

Deehan: Lieutenant Governor Karyn Polito, his number two, really is the likely contender. Her fundraising is through the roof right now. She's definitely prepared to run because it is an open question whether or not Governor Baker will decide to run again for a third term. He very well might say 'I'm done.' Then we also have former U.S. Senate candidate Geoff Diehl from Whitman, who pretty much got destroyed by Elizabeth Warren in 2018. But he's polling in this Republican-focused poll just a smidge lower than Polito is. They're kind of neck-and-neck. A lot of that is about name recognition. We don't really know if any other Republican candidates would come out of the woodwork. But if Polito runs as a moderate-style, Baker-style Republican versus Diehl, who's very much aligned with the kind of Trump wing of the Massachusetts party, you could see a definite culture clash in the GOP before we even get to a general election.

Mathieu: How did Polito come in this poll?

Deehan: Well, Polito's got 22 percent and Diehl is 21.5 [percent], I believe. So it's a lot of room.

Mathieu: What should we make of those numbers, Mike? Republicans are not happy with the vaccine rollout, but the general public once we get into the general is supporting Baker.

Deehan: And that's exactly it. What do we make of this? It seems like primary voters again, the most partisan, the most interested don't like either side of it. Republicans don't really like what's going on with the vaccine rollout, but they do like the business reopenings. The Democrats don't really like either of them, even though a lot of Democrats still do like Baker. So if Baker were to run again, he might have a challenge in the GOP primary, whether it's Diehl or somebody else. But the general public does seem to really like him. Like we said before, 74 percent from most residents. So any Democrat hoping to take him on is going to really need to hope that there is that Republican primary fight either against Baker or splitting the party if Baker's not there, that forces whoever the candidate is, Baker or Polito, to run as more conservative than they've been in office [and] paint them as more Trumpian and more conservative. That's what a Democrat wants to do. But they also have to hope that by November 2022, voters have another reason to replace Baker or replace the Baker Administration because this vaccine saga might very well be over by then. The pandemic could be over [and] we could be on to other more typical things.