Really ?
He has 40% or thereabouts absolutely locked down, a combination of a smaller number of GOP loyalists who would vote for any candidate the GOP puts up regardless of their personal feelings towards them and a much larger group of Trump fans who think that he can do no wrong. These people are highly motivated and will turn out to vote.
Then there are people who may not be Trump fans but who have done fine under the Trump administration as the economy has ticked along. They will vote to maintain the status quo (and would have done so if a Democratic Party President were in power) but they may not be super-motivated to go out to vote.
The GOP is actively undertaking voter suppression in key states to ensure that as few people who are likely to vote Democrat are able to do so. This may only have a marginal effect, but in some key states that's all he needs. It doesn't matter how many millions he loses the popular vote by (and of late GOP Presidents have made a bit of a habit of losing the popular vote), as long as he gets the electoral college votes from the swing states, he's reelected.
The other side of the coin is whoever ends up being the Democratic Party candidate running against him. Unless this candidate is a Bill Clinton or Barack Obama, people may choose to stay at home rather than turn out and vote for an ageing party apparatchik. "Not Trump" may not be a good enough message.
Right now, and in the absence of a charismatic Democratic Party candidate and/or an economic downturn, IMO Donald Trump is highly likely to be reelected. Anyone who actually cares enough about impeachment enough to pay attention is already anti-Trump and has been from day 1.