It doesn't matter how "fired up" they are, as long as they can only vote once, the Democratic candidate should have a good shot in 2020. I say this all the time but it's true, Trump won the election (vs an admittedly weak opponent) by virtue of 105,000 votes spread across the 3 states which decided the election:
Michigan - 16 electoral college votes (Trump won by 12,000+)
Wisconsin - 10 electoral college votes (Trump won by 24,000+)
Pennsylvania - 20 electoral college votes (Trump won by 68,000+)
Those 3 states combine to have 46 electoral college votes. Add them to Hillary's total of 226 and you have 272. Take them away from Trump's total of 304 and you have 258. So, basically, Trump defeated a historically weak candidate by slightly over 104,000 votes.
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And also, look at Trump's poll numbers. His Real Clear Politics average is currently at 43.7%. He is under water in every poll. Even Rasmussen (which leans right) only has him at 46%. There is no indication that he has extended his base of support since the election on November 8, 2016.