I'm (very seriously) trying to understand how backing something with >2/3 open support, that's clearly bipartisan, would hurt one's political career. I'm guess

I'm (very seriously) trying to understand how backing something with >2/3 open support, that's clearly bipartisan, would hurt one's political career. I'm guessing maybe it's because although those who oppose some form of marijuana (neither medical nor recreational) are in the minority, they still make up a sizable voting block when an election is won on the marginal vote. But how does that play out when >2/3 of people support it across the board, and that politician is the only one doing something to push it forward? That politician would literally be the only choice if marijuana is meaningful enough to a voter. So while the politician may lose some supporters, would they not gain support from others?