Final answer:
The most serious issue according to Dr. Rush was the coronavirus pandemic (COVID-19).
Step-by-step explanation:
According to exit polls from the November 2020 election, where Donald Trump was defeated in his bid for reelection, COVID-19 was the third most important issue to voters, following the economy and racial inequality.
In exit polls, 17 percent of respondents indicated that the coronavirus was the most important issue affecting their vote, making it the third most frequently mentioned issue behind the economy and racial inequality.
Of the participants who viewed the pandemic as the most important issue affecting their vote, a substantial majority of 81 percent cast their vote for Joe Biden.
While President Trump's handling of the pandemic was not the sole reason for his defeat, it was a significant factor, as 55 percent of respondents before the election felt that the handling of the pandemic was a very important issue in how they would decide to vote.