Mamchin hasn't been as on board with the far left social agenda as the rest of his party (or a lot of Republicans) have been. He might tell you that he's not as keen on abortion and other policies of his party because of the "compassion" he claims to have.
If lived in his state I'd vote for somebody more conservative, but through the years I've also found that people celebrated as conservative (Dick Cheney, Paul Ryan) have also been wrong and not worth very much.
Joe has compassion for whatever fattens his wallet or gets him votes. I appreciate when he McCains the Dems in the back, but he's still a slimy weasel. Just look how he wobbled on impeachment until his vote didn't matter. Or stuff like this:
He's might be better than Murkowski and maybe Romney but it's close.