Conventional wisdom tells us that Democrats benefit from higher turnout in presidential election years. Their key voter blocs, like the young and people of color, are more likely to vote in presidential elections, as opposed to midterms.

Ergo: Expect the DFL's sweeping 2018 victory to be a mere preview of 2020, when even more of these voters will show up.

Not so fast.

Some analysts see signs in the 2018 election that supporters of President Donald Trump stayed home, and they expect them to show up in 2020.

"The GOP was unmotivated in 2018 [a common problem for the party in the White House during a midterm election]. They are now super motivated," GOP activist Gina Countryman wrote me in an e-mail. "The Democrats were already ready to walk on glass to vote in 2018, so while I expect more Democrats to turn out, the room and likelihood of growth is on the right." She points to the Trump campaign doing data work to identify non-voters who are Trump supporters or potential supporters and registering them, which is a bit unusual for Republicans but could pay dividends.

Todd Rapp, a former DFL activist who is now a public relations executive, sent me some relevant data.

In the Fourth and Fifth congressional districts, which comprise the Twin Cities and are heavily DFL, about 36,000 fewer people voted in 2018 than in 2016. In the Second and Third districts, which are, respectively, purple and blue, there were 62,000 fewer votes than in 2016.

The drop-off in Republican districts was much larger. In the First and the Eighth, 88,000 fewer. In the Sixth and the Seventh, 93,000 fewer.

Bigger drop-offs in the red areas of the state in 2018 might indicate Republicans have more room to grow in 2020.

But Rapp also raises a compelling demographic point: Between Election Day 2018 and Election Day 2020, about 140,000 young people will have turned 18, while about 60,000 older voters will have died.

Young people tend to vote DFL; older people tend to vote Republican. (This isn't Chicago — the deceased can't vote.) Advantage: DFL.

Jeff Blodgett, a DFL activist, finds it unlikely that turnout will be up on just one side — both sides are extremely energized. Polling supports that view. He acknowledges, however, that a Republican presidential candidate investing heavily in Minnesota is a new phenomenon and a potential wild card.

Minnesota turnout in 2008 was about 78%. In 2016 it was about 75%. If we get to 80%, who are those 5% who show up next year but didn't vote in 2016? Are they the working-class whites from whom Trump has commanded such loyalty? Or are they young voters and people of color whose passionate distaste for Trump is equally motivating?

Finally, there's another group we should address: About 277,000 Minnesotans voted in 2016 but chose neither Trump nor Hillary Clinton. That's a lot of votes.

J. Patrick Coolican 651-925-5042 Twitter: @jpcoolican patrick.coolican@startribune.com