First, Trump knows that gaining the support of a majority of voters in a presidential election is not a requirement; its simply an aspiration. In fact, two out of the last three presidents were elected despite losing the popular vote.
Second, the continued decline in support for both political parties works to Trumps advantage. The lack of voters faith in both parties increases the probability that there will be a major third-party candidate on the 2020 ballot. It will also lead to other minor-party candidates joining the presidential race. The multi-candidate field will further divide the anti-Trump vote, making it possible for him to get reelected simply by holding on to his current level of support.
Third, despite dismal poll numbers, Trump enters the contest with a job approval rating that is certainly at least marginally better than what the current national polls would suggest. Throughout the 2016 election, most analysts tracked the national polling, which failed to capture Trumps strength in key battleground states. Current surveys continue to understate his support. Many national polls survey all eligible voters, rather than registered or likely voters, which can underestimate Trump, and some voters may be reluctant to admit that they are pro-Trump at all. Add to that the fact that Trump effectively demonstrated during the 2016 campaign that he is capable of expanding his support by effectively demonizing his opponents.
