Per the average of all polls on Nate Silver's FiveThirtyEight site (and I use them, because Silver is not a pollster himself, but he is a respected statistician who analyzes polls - and he uses a much larger sample size than Real Clear Politics):
Michigan
Joe Biden (D) ............. 51.4% (plus 8.7)
Donald Trump (R) .... 42.7%
Minnesota
Joe Biden (D) .............. 50.4% (plus 8.4)
Donald Trump (R) ..... 42.0%
Pennsylvania
Joe Biden (D) ............... 50.1% (plus 5.1)
Donald Trump (R) ...... 45.0%
Wisconsin
Joe Biden (D) ................ 51.9% (plus 8.6)
Donald Trump (R) ....... 43.3%
There is not a path to 270 electoral college votes for Donald Trump without winning at least one of these 4 states. Biden's lead has been consistently outside the 4.5% margin of error in these states, over the last month of the campaign, and unlike Hillary Clinton in 2016, Biden has been consistently polling over 50% for over a month now in these states.