Well, I'm not really sure Pyroclastic Ash and Debris would hit the 270 electoral college votes needed to win the election, since most of the states outside of its campaign range would likely not vote for it. This would push the vote for president to the House, where Pyroclastic Ash and Debris has no members of their party to vote for them, resulting in a Trump victory, with the Senate picking the VP, where I'd assume they'd agree on Pyroclastic Ash and Debris' running mate.
This eruption would eliminate three quarters of the map, eliminating a majority of the republican electors' counties and kill all 40 voters responsible for that majority.