One reason I think Trump/Vance could lose is they are both very polarizing figures. Both have taken positions which not only offend much of the American electorate (the common man/woman), but the Business and Social Elites as well. While Trump is a threat to their power structure, Vance has not exactly made friends with them either and has attacked Wall Street even if nobody loves them, they have power and clout.
So they've made some critical errors already and alienated traditional allies who might otherwise support the Republican Party. That alone could send droves of funding over to the Democrats.