A quick note on polls ... I read recently that Republicans are very confident (some more confident than 2016) in spite of poll numbers in swing states showing there might be a problem. The reason? The 2016 election showed that Trump supporters disproportionately hang up when called for polling. This results in an oversampling of Democrats. Also, some people simply lie when polled. The article quoted someone as stating that they actually answered the opposite of what they really believed to throw the pollsters because "they didn't like some of the questions they were asking me".
In a data driven world your decisions are only as good as your data quality. That makes political polling a hard business to be in right now.
The polls don't look great for Trump. 538 does a good job of aggregating all of the incoming poll data.
https://projects.fivethirtyeight.com/polls/
https://projects.fivethirtyeight.com/trump-approval-ratings/
The second thing driving confidence is the expectation of a revival in the economy leading INTO the election. We will see if that confidence is founded.