It will be hard for Trump to get reelected with his current approval rating unless he faces another candidate as unpopular as Hillary Clinton. I don't think the democrats will nominate another Hillary (40% favorable 55% unfavorable) Clinton-tier candidate, but maybe they will nominate a Romney-tier candidate (i think he was around 45% favorable 50% unfavorable?). That said, there's still 3 more years for his approval rating to go up, although I am skeptical he will be able to recover. If his approval rating goes up to 45%, I'd give him a 50% chance of getting reelected. It seems as if Trump has lost the most support in three states that were key to his victory -- PA, Michigan, and Wisconsin, so that will make things challenging.
If Trump is at 45% on Election Day, that would indicate he has taken significant actions to win over dissatisfied moderate Republicans and independents and has performed somewhat competently. Considering his campaign will perform a character assassination on whoever the Democrats nominate, like Sanders and Trump did to Clinton in 2016, I think 45% approval ratings would almost guarantee a Trump victory.
That being said, I highly doubt that happens. I think just about every potential Democrat would be somewhat popular in a general election and would be able to defeat Trump. Assuming he is still president and is on the ballot, I think he loses by an Obama '08 margin.
