Most polls have shown the opposite, more people saying they voted for Clinton. MC is the only one I've seen regularly have a Trump lead.
I don't know exactly what that speaks to though - whether they are over-polling Clinton voters or Trump supporters are saying they voted for Clinton. I do remember this becoming a topic in 2016 when there was that poll that kept contacting the same people to see how their vote choice shifted over the campaign, and it was initially based on who they previously voted for in 2012, which brought up questions of why the 2012 support samples were not representative of that election. Although I could have it backwards in who people are most likely to say they voted for - the winner or the loser, maybe depending on how they view the actual winner (eg, disapprove/approve).
At any rate, I'm no expert on it, just regurgitating what I've read 
I believe the standard thing is that people misremember their past vote to be what they currently wish it was. So winners go up right after elections but if people turn on the incumbent you'd see the opposite.
