Buried beneath all the drama and ugliness of this election is a truth I don't think many people have examined: if Trump wins the election on Tuesday, it's going to be very bad for Republicans' prospects as a viable party long term. Whether they win or lose, fundamental realities of their fractured coalition will call that question eventually, but if Trump loses, the Party will hang together as an oppositional force against Hillary Clinton.
During the Obama era, Republicans honed their skill at outrage and obstruction, the key pillars of any effective opposition party. With none of their actual policy goals at stake, it was easy to stay united. But if Trump wins, the GOP can't stay an oppositional Party. It would, in the event of a Trump win, almost certainly, hold all levers of government. Policy accomplishments now become the prize of power, and realizing them will expose the warring factions' differing goals. Once a strong coalition of a corporate donor class, religious conservatives, and neoconservatives, a post-Trump GOP would be guided by Trumpies (fueled by racial grievance, in favor of social welfare programs, and opposed to trade and foreign adventures). The voter base that supports these positions was drawn from the previous coalitions, leaving them all weaker--and in the case of the donor class and neoconservatives, in direct conflict with the base.
There might be a few issues they could come together on, like guns, abortion, and coal, but these are mostly not the groups' top issues. Worse, issues like nullifying Obamacare are riven with danger, since the GOP's misinformation campaign has obscured all the benefits people have under its provisions. But it's more likely that Paul Ryan and Mitch McConnell will push the issues they always have--massive tax cuts for the wealthy, new trade deals (it's high on the party platform), re-deregulate Wall Street, cutting future benefits to Social Security and Medicare, and radically slashing social programs. None of these things will be popular with the Trumpie base, and where will all that white resentment go if the GOP don't immediately pander to it?
Then there's the issue of Trump as president. It is frankly inconceivable to think of a non-catastrophic Trump administration. The best-case scenario is a shadow government headed by traditional GOP elites, perhaps lead by Mike Pence. Even in that scenario, it's impossible to imagine President Trump not saying things that embarrass the party and enrage allies. There are many scenarios of disaster--too many to speculate on.
After a year of in-fighting and bad leadership, the midterm elections would force the divisions wide open. Primary challengers will emerge both for and against the Trump loyalists. If Trump loses, the Party can forestall the reckoning. (Maybe.) But if he wins, the reckoning begins in a few weeks' time, as the coalitions gear up to seize power. No one is thinking about this now, but I don't see how any other outcome is possible. The Republican Party might survive a Trump candidacy; surviving a Trump presidency will be much, much harder.