Polling from Morning Consult illustrates well the limitations of Trump’s base-only strategy: his support (base and supportive voters) represents less than needed for re-election. That support is, in fact, notably consistent in its inadequacy:
Over many months, including before the brunt of the pandemic, Trump has been stuck in a weak position. This does not mean that he cannot be re-elected if conditions change; it means that he is (and obviously has been governing) as a minority president imposing himself on a larger, opposed number of Americans.