Down 12%? That is high even for recent polling. It could be right if Trump support is crashing. Sometimes new polls show that. How can I tell? I am likely to see a new poll out of the recent range as an outlier instead of reality.
People closer to a Reagan-Bush I orthodoxy might see Donald Trump as a ruthless, unscrupulous, and capricious demagogue. Hillary Clinton, as Secretary of State during the first term of the Obama Presidency now 'owns' the foreign policy, which is nearly identical with Bush I foreign policy. It will take a long time for the cautious foreign policy of '41' to fail.. but not long for a Trump foreign policy to fail.
It's hard to find an analogue for this Presidential election. At first I thought of the essentially-binary contests involving Barack Obama, with the electoral map looking like 2008 or 2012 with a tweak or two. But we can't now ignore the Libertarian candidacy which includes two veteran politicians who have been Governors of states.
Gary Johnson is going to take far more votes away from Donald Trump than he and Jill Stein (Green) will take from Hillary Clinton. The Trump campaign is a mess because the candidate is a mess. It's possible to win on platitudes, but only if those platitudes (like "Tippecanoe and Tyler too" or the 'normalcy' of Warren G. Harding) do not offend. If those platitudes offend, then they are brittle targets.