Anyone writing him off this early is either delusional or has zero exposure to Maryland politics. This is not Bredesen vs. Blackburn. He is exorbitantly popular, moreso among Democrats and independents than Republicans, and the Maryland Democratic party -- arguably one of the most pathetic in the nation -- has run screaming in terror from him every chance they have had to put an end to this nonsense. I have complete faith in my party to utterly drop the ball on this one.
Look at the Massachusetts Senate race in 1996. Bill Weld was a straight-up liberal who was also super popular with Democrats and independents and had just won reelection with 70% of the vote. Despite that, he still lost the Senate race, and ticket splitting happened a lot more in 1996 than it does now. Trump will lose Maryland by at least 33 points, and as broadly popular as Hogan may be, he's not going to make up that gap.
To add onto this, large chunks of the Dem base is made of groups that just don't really split ticket federally; ultra-white college ed liberals and a large population of black voters.
I think there's a decent number of moderates and liberals in Maryland who may personally like Hogan to some extent but won't vote for him because Senate control is more important.