In 2016 Clinton lead all the dozens polls (except 2 polls of LA Times)  including 358, and won by 3 million votes of the popular vote. However, several thousand votes in some key states in the American agricultural and industrial Midwest, the states which give the crucial Electors, gave Trump the victory.
This year the surveyors repeat this error. Biden has the lead in the national count, sometimes by a double-digit gap, but this lead is irrelevant, many of the swing states lean to Trump, some in a 4% lead, including key states such as Ohio or Midwest states such as Iowa, Missouri and Arkansas. Trump doesn’t need all these states to get reelected. it’s enough for him to take Texas of Florida, in which the gap in the polls is statistically insignificant. Yet, the liberal media is sure that Biden is to be elected, as it was sure in 2016 that Clinton will be. Why?
In many respects, there are two Americas, with no connection between them. The agenda of the liberal media in the west coast and the north-east are the Coronavirus and the public health system. The conservative media in the south and center of the US has other agenda: the fear from the liberal tendency to give refugees’ children immunity from deportation, to give te refugees social security and citizenship, to afford them not mentioning citizenship in the referendums, and cut the budgets of police forces. The white conservative voter in the midwest and some of the border states with Mexico is appalled by this liberalism. This fear is what brought Trump to power.
Even if Biden wins NY, New England and the west coast, like Clinton in 2016, the crucial states are in the sout and the midwest. The coronavirus is marginal there. It is considered mainly as a Chinese invasion or fake news. The deaths from the pandemic is mainly in Democratic strongholds, Ny and CA, or in urban centers in FL and TX, regions that anyhow vote for Biden. The conservative vote will hardly change because of the coronavirus. They hardly feel this pandemic.
In addition, there are some problems with the polls, problems that make them biased in favor of the Democrat candidates. From ideological reasons, many don’t answer the pollsters. The polls of the liberal press are considered as representatives of the establishment in Washington, and the voters of Trump, who rose as an anti-establishment, suspect the establishment (or the press and the survey institutes, that are considered as a part of it), and do not cooperate.
Many Republicans don’t answer the pollsters because of economic reasons, too. A person that responds to pollsters is mainly well-to-do, lives in the suburbs, and has time, will and ability to answer polls, the register for vote, obligatory in the US [I added in the Hebrew origin], which means losing a day salary, and losing another day’s salary in order to vote, because in the US the election day isn’t a holiday. Democrats answer polls more, because they are more at home than poor Repubican whites from the Rust Belt and the Bible Belt states, who need to work a long, two shifts workday, and are less available at home to answer pollsters. This way, their support of Trump goes unnoticed in the polls.
The economic problem makes it difficult for the pollsters in another way: many poor Blacks can’t register for vote, because they will be fired if absent from work for that. They can answer in the polls they support Biden, but if they don’t vote, it’s another false leaning in favor of Biden in the polls.
The conservative right presents polls that lean against Trump in order to encourage conservative vote. (In Israel, PM Netanyahu did the same while he declared in election broadcasts, “Arab voters are heading to the polling stations in droves”.)  In the sixties it was called “Southern Strategy”: make whites fear of Blacks, in order to move white conservative voters to the ballots.  Today, those who are considered as a danger, are South American immigrants, Hispanics and Puerto Ricans in addition to Blacks, but the tactics is the same. Therefore, because of fear from Blacks, liberals, and those who are considered as anarchists, leftists and communists (yes, 30 years since the Communism collapsed, and there is still fear of Communism in America), fear that the race riots only strengthen, even conservative voters that are ashamed to admit they vote for Trump (as happened in 2016), nevertheless will vote for him.
History is with Trump: in the last 22 presidential elections, in the last 90 years, an incumbent president was reelected 10 times. Only 2 elected presidents were not reelected in the next elections, and were a one-term presidents: Carter in 1980 (lost to Reagan) and Bush in 1992 (lost to Clinton). Incumbent presidents who lost elections, lost mainly because of the economy. In the presidency of Trump, until the pandemic, the economy improved, If the current deterioration in the economy was in ordinary era, Trump wouldn’t have been reelected. But Trump uses the crisis in order to upgrade himself and pose as a wartime president. He repeats over and over again the say “the Chinese virus”, as if the pandemic is a Chinese attack. Almost every president who lead in times of war, was reelected: Truman after WWII, Eisenhower who lead in the Korean War, LBJ during the Vietnam War (even though he was reelected mainly due his social reform; it seems that the war only damaged his popularity), Nixon in Vietnam and GW Bush in Iraq. Trump presents the crisis as a time of war, and hope the effect of the image of war will make the public unite behind him again.
And last but not least, the undecided: in most of the polls, Biden doesn’t cross the 51%  and it is well known that voters tend to repeat their patterns of vote. i.e., reelect Trump. On this background, the double-digit advantage of Biden in the polls might be totally eradicated in the election day. Remember Hillary.