Jennifer Carnahan kicked off her re-election campaign to be Republican Party chairwoman last week, promising GOP delegates that her work building grassroots infrastructure, hiring steady operatives — most recently Becky Alery — and an improved national landscape will lift Minnesota GOP fortunes in 2020.

Can Republicans come back in 2020 after losing every statewide race and the Minnesota House?

History suggests presidential elections are both better for Minnesota Democrats and far less volatile than midterms, as recently noted by a memo to incoming House Speaker Melissa Hortman and Majority Leader Ryan Winkler, written by Democratic lobbyist Brian Rice.

Minnesota House elections are a decent proxy for the overall mood of the electorate. Democrats have gained Minnesota House seats in 11 of 17 presidential elections since 1952. In two others they neither gained nor lost seats.

When Democrats gained seats, they picked up an average of six, while Republicans flipped an average of four. This isn't surprising given Minnesota's long history of siding with the Democrat in presidential elections.

Midterm elections have been much more volatile. In the 17 midterm elections since 1954, the average gain of the winning party was 16 seats. Indeed, in 2018 the Democrats picked up 18 seats.

Only in the 1984 election, in which Minnesota barely chose favorite son Walter Mondale, did Republicans pick up a substantial number of seats — 12.

Republicans can take some comfort in President Donald Trump's 2016 performance here, in which he lost by the smallest margin of any Republican since Ronald Reagan in 1984, and Republicans picked up five Minnesota House seats.

The problem is that Trump was helped by the weak candidacy of Hillary Clinton. But he barely improved on the raw vote total of Mitt Romney in 2012. Moreover, polling — and the 2018 election results — would seem to indicate his support here has degraded badly.

Rice and co-author Frankie Johnson warn that "past results are no guarantee of future performance." A Trump resurgence could change the dynamic. Or, Democrats could be harmed by "a significant political problem that develops in the state that is a direct result of action by DFL legislators."

Which is an oblique way of warning Hortman and Winkler that bad policy — or high-profile personal scandals — make for bad politics.

Much is at stake. If Democrats keep a seat being vacated by Tony Lourey, who is Gov.-elect Tim Walz's pick to be commissioner of the Department of Human Services, in a February special election, they'll be just one state Senate seat away from full control of state government. And, they would be consolidating that control at the perfect moment: Redistricting, when lawmakers and Walz will be drawing new congressional and legislative maps.

J. Patrick Coolican 651-925-5042 Twitter: @jpcoolican