Here's just a straight average of national polls in years with incumbent presidents on the ballot. President Trump's numbers are worse than Jimmy Carter's at this point during the 1980 presidential campaign, nearly as bad as Gerald Ford's in 76. Not exactly in great company... 
Here's the same graph but for the full election year and only since 1980. You can see that game-changing events DO happen between now and the election, but they're very rare.
3/3 And if you limit the graph to just the polarized era, you can see that Trump's numbers are pretty unprecedented.
Since 2000, no candidate has ever come back from this type of position in the public polls.
Since 2000, no candidate has ever come back from this type of position in the public polls.
