With less than three months remaining before Election Day, what do polls tell us about the current state of the presidential campaign?
Most high-quality national polls taken within the past few weeks show Joe Biden with a 7-to-9 point lead over Donald Trump. The 538.com average of national polls, which makes adjustments for each poll’s sample size, quality and recency, showed Biden with a 7.8-point lead at the end of last week. This is down slightly from Biden’s largest polling lead of the election cycle, 9.1 points on July 15.
Polls also indicate that the most common frame through which voters are looking at the election is as a referendum on Trump. Biden’s lead in the polls grew in late spring and early summer as Trump’s approval dropped. Most high-quality polls taken recently show that about 55 percent of those questioned disapprove of the president’s performance, 10 to 15 points higher than those who approve.
Trump’s approval rating has fallen among all demographic groups since March, when coronavirus cases began to increase in the United States. According to Gallup Poll data, Trump is currently viewed positively by only one group of voters: white people who did not attend college. Groups that had approved of Trump for the first three years of his presidency — men, residents of the Southern states, and people over 65 — have all turned negative on him in the past five months.
Polls in key states show that, at this time, Biden has more pathways than does Trump to a majority of 270 or more votes in the Electoral College. However, a repeat of 2016, with Trump losing the popular vote and winning the electoral vote, cannot be ruled out. 
Michigan, Pennsylvania and Wisconsin were the three states that gave Trump an electoral vote victory in 2016. As of the end of last week, the 538.com averages of state polls showed Biden up by 7.8 points in Michigan, 7.5 points in Wisconsin and 6.1 points in Pennsylvania.
The Trump campaign may be pulling some resources out of Michigan. Biden, a native of Scranton, may have a home-state advantage in Pennsylvania. Wisconsin, a state where there have been recent Republican attempts at voter suppression, may end up being the closest of these three states, and could be the tipping point state in the nation.
If Biden were to win all the states won by Hillary Clinton in 2016, plus Michigan, Pennsylvania and Wisconsin, he would have 278 electoral votes. If Biden won only Michigan and Pennsylvania, he would be at 268 electoral votes.
The most promising state for a switch to Biden from 2016, outside of the Midwest, could be Arizona, with 11 electoral votes. This state has undergone demographic change in recent years, with the electorate becoming younger, and with Latino voters making up a larger share of the voting population. Biden may also benefit from a reverse-coattail effect from Democratic Senate candidate Mark Kelly, who polls show is well ahead of Republican incumbent Martha McSally. The 538.com average of Arizona polls showed Biden with a 3.6-point lead in the state as of last week.
North Carolina is another possible state for a Trump-to-Biden switch. Like Arizona, it has been undergoing demographic change, and has a strong Democratic Senate candidate, Cal Cunningham, who is challenging Republican incumbent Thom Tillis. The 538.com average showed Biden leading by 2.1 percent in North Carolina through last week.
Democrats say that Florida polls — which show Biden ahead by about 5 points — indicate that the Sunshine State could flip from 2016. However, like Wisconsin, Florida has a history of voter suppression by Republicans. For Biden to win Florida, his campaign would have to undertake a massive mobilization and turnout effort, especially among the diverse population of southern Florida. A similar effort would be required for Biden to win in Georgia, a state where the polls are basically tied.
Eric L. Davis is professor emeritus of political science at Middlebury College.