Trump's currently trying to antagonize Iran into war. Once we have a fresh shooting war Trump's win in 2020 is pretty much in the bag. He'll ramp up the fear and terror to new heights.
Like George W., he's treating the security briefings entirely too lightly. Justified or not, failing to act on Clinton-era intelligence is considered by some to be one of the contributing factors to the 9/11 terror attacks. If Trump presides over a terrorist attack on US soil he's going to be VERY difficult to defeat in 2020.
He's not going to be impeached. By the time the mid-term elections come around, he'll have so much Fear, Uncertainly and Doubt in play the Democrats will probably lose seats, not gain them. Anyone hoping the GOP will impeach him is living in a fantasy land. They'll probably try to contain the damage he does to their brand but in the end, a powerful populist leader typically leads to more power for his party.
The real questions in my mind are not if Trump will be a two-termer. What I wonder about is:
Will Trump get a constitutional amendment passed to remove the POTUS term limit and allow himself to run for a third term?
Will Bannon be able to continue dancing the line between white supremacist ideologies and "I can't be racist, I'm a Jew!" to avoid being targeted for assassination by the more overtly NAZI portions of the Alt-Right? While the Alt-Right turning aginst him and successfully assassinating him is unlikely, it's still close enough to the realm of possibility that Bannon would be a fool to not prepare for the contingency.