According to 538, Trump's approval has risen a little less than 3 percentage points since August 1st and is currently at 43.8%. It has not affected head to head polling. Why has this happened?
Fluctuations in polls are difficult to analyse, especially when polls just report a headline figure, rather than drilling down into specific topics, and it can be hard to tell whether an increase is significant or not. However, there does appear to be some evidence to suggest that this rise in approval you have observed is in part related to an improved view of Trump's response to the COVID-19 pandemic during August. Some observers suggest that more recent fluctuations relate to his response to the Supreme Court vacancy in September, as well as his debate performance at the end of the month, although only a few polls have been conducted since that event.
Although Gallup maintains that this increase is not statistically significant, it does seem to hypothesize that President Trump's response to the Supreme Court vacancy may have affected his approval rating:
Although the increase of four percentage points in Trump's latest rating is not statistically significant, the poll's internals suggest a rise in his support the second half of the Sept. 14-28 field period coincident with Justice Ruth Bader Ginsburg's death and lying in state, as well as Trump's announcing that he would quickly make a nomination to the Supreme Court. This suggests that some viewed his handling of the situation positively.
Looking at the full tables from Gallup, we can see that since the beginning of August, Trump has improved his approval rating across all categories - with regard to the economy (+6), foreign affairs (+5), the COVID-19 pandemic (+8), relations with China (+6), race relations (+1) and crime (+2).
The October 1st daily approval ratings analysis from Rasmussen Reports, however, makes the opposite observation to Gallup - that Trump's approval rating dipped following his SCOTUS nomination, but is now on the rise again - apparently as a result of his debate performance:
This survey is the first to include a night of polling following the first presidential debate between Trump and Democrat nominee Joe Biden. The president's approval ran in the low 50s for 10 days through the end of last week but dropped as low as 46% in the first three days of this week following his nomination Saturday of federal Judge Amy Coney Barrett to the U.S. Supreme Court. Now his approval appears to be on the rise again. By next Monday morning, all 1,500 voters in the daily tracking survey will have been polled following Tuesday night's contentious debate.
On a more issue-specific level, the September 2020 Executive Approval Update from the COVID-19 Consortium for Understanding the Public’s Policy Preferences Across States found that during August, Trump's approval with regard to his actions on the pandemic rose despite gubernatorial approval ratings falling, suggesting that he has made up some ground on this issue.
The August wave of our COVID States survey indicates a continued gradual decline in approval of governors’ management of COVID-19, and a small improvement in President Trump’s management of COVID-19. The average governor saw their approval slip another 3 points in the last month, to 48% approval (versus 63% in late April). President Trump, who started from a much lower point, rebounded slightly from his low point of approval of 32% in July to 34% in August.
First point: most polls aim for a margin of error of around 3%, so rising or falling by that amount is indeterminate: it might reflect a real change, or might merely be a statistical artifact (i.e., a random fluctuation of the distribution of the sample chosen, not of the underlying population).
But giving the statistics the benefit of the doubt, it's worth nothing that:
- Roughly mid August (see this timeline), Trump began changing his messaging on Covid-19, promising a quick vaccine and acknowledging the severity of the pandemic
- In late August, the Republican National Convention began, giving Trump significant positive air-time, and reaffirming his role as the GOP choice
Either of these could be expected to boost Trump's approval rating (at least within his base, and among those who are still undecided). In fact, it's somewhat surprising that Trump did not see a more significant boost from the latter. Conventions are typically the high-water mark for incumbent approval ratings before the election, since the remainder of the election season generally becomes a protracted critique of their term of office.