Really depends on how Brown campaigns. Running for Senate and leaning on statewide issues won't work when he's trying to appeal to voters in, e.g., Colorado, Florida, New Hampshire (not to mention national donors) as a Presidential candidate.
All things considered I'd put odds at 4-1 that Trump would win this state.
I think this is fair - Brown is still competitive in OH because he has been successful in divorcing himself from the national party, which would not be possible if he is the nominee. It of course depends on what issues become most important/the national environment, but in a 'neutral' year I would put it at Tossup/Tilt R, with better odds for Brown than you give but still favoring Trump.
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