In state after state, Democrats have been swarming the polls and swamping GOP turnout increases.

“It all comes down to turnout” is the hoariest truism in election coverage. We don’t yet know what it will be for the midterm election, but based on turnout for the primaries concluded in 2018, Republicans should be worried. The much talked of “blue wave” could very well be bearing down on the party.

In recent cycles, primary turnout has translated decently to the national vote for the House. The exceptions, 2004 and 2012, involved an incumbent president running for reelection. Midterms do not suffer from that problem (though individual state and district races may). Competitiveness will depend on how winnable politicians think elections may be.

The 2018 primary turnout numbers should alarm the GOP when compared with recent midterm “wave” elections. Before the 2006 blue wave, Democrats received 54 percent of 24.4 million primary votes. Before the 2010 red wave, Republicans won 56 percent of 28.5 million primary votes. In 2014, the GOP got 55 percent of a lower 23.9 million primary votes.

In 2018, even before the New York primary, Democrats won approximately 53 percent percent of an astounding 35.7 million primary votes. The Democrats have swung to a near 2006-level primary edge amid a 47 percent increase in overall turnout.

The leap from 2014 reflects an increase in competitive races. As of July, the number of contested House seats had risen from 251 to 340, overwhelmingly on the Democratic side (conversely, there were a record number of retirements on the GOP side). The number of open gubernatorial seats jumped from four to 20. And the Senate map enticed Republicans looking to unseat red state Dems. The result? Republican turnout was up 25 percent from 2014, but Democratic turnout increased 75 percent. Accordingly, the Republican vote share fell almost everywhere.

There are only eight states where GOP primary turnout increases outpaced Democratic increases, three of which are of particular interest.

First, in North Dakota, where Republicans seek to oust Sen. Heidi Heitkamp, GOP turnout rose 40 percent and the party’s vote share rose a few points to 65 percent, as overall turnout rose 34 percent. Heitkamp ran unopposed, but the gap signals her likely weakness.

Second, in West Virginia Republican primary turnout shot up 61 percent (versus the Dems’ 20 percent rise) as several candidates (including Don Blankenship, who gave us “Cocaine Mitch” McConnell) competed to face Sen. Joe Manchin. But the Dems’ overall 54 percent primary vote share suggests an uphill fight in a still-evolving state.

Third, the Wisconsin primary was a barn-burner, with the GOP pumping up its vote by 90 percent. But dairyland Dems’ turnout increased 73 percent and secured 54 percent of the primary vote. No wonder Gov. Scott Walker, a veteran of tough elections, has been worried all year.

Ironically, Wisconsin may be the best news for Republicans in the Midwest. In Illinois, with a troubled governor and at least two toss-up House races, GOP turnout dropped 12 percent, while Democratic turnout spiked 170 percent with a 65 percent overall vote share. The stakes are similar in Iowa, where Republican turnout sagged 36 percent, as Dems surged 154 percent to a 64 percent vote share.

There are another two toss-up House races in Michigan. The GOP boosted turnout there by 60 percent, but the Democratic turnout leapt by 120 percent to a 53 percent vote share. In Minnesota, where there are four House toss-ups, Republican turnout jumped 74 percent … but the Dem turnout rocketed 206 percent to a 65 percent vote share.

The Rust Belt is a mixed bag. In bellwether Ohio, GOP turnout rose 31 percent to the Dems’ 41 percent, but the Dems’ 45 percent total share suggests good Republican candidates may survive. In Pennsylvania, GOP turnout upticked slightly from 2014 (an uncompetitive year), but fell 12 percent from 2010. Competitive races for Congress boosted Democratic turnout in 2018 enough that Sen. Bob Casey and Gov. Tom Wolf won more votes in uncontested primaries than were cast in the GOP contests to face them.

In the North Atlantic, Maine Republicans have a governorship and a House seat at stake; their 65 percent increase in turnout was beaten by the Democrats’ 103 percent spike and 56 percent vote share. In New Jersey, three House seats may be winnable but the GOP’s 43 percent rise in turnout was beaten by the Dems’ 89 percent increase and 64 percent vote share.

In the South Atlantic, Virginia is tough to assess, because it does not hold primaries for uncontested races. But the GOP took losses in the high-turnout 2017 elections.

Florida remains competitive. The GOP’s 71 percent turnout increase fell short of the Dems’ 81 percent, but the Democratic vote share was 45 percent overall. Georgia’s hyped Democratic primaries produced a nice 69 percent turnout surge, while the GOP was flat — but the Dems’ vote share was held to 48 percent and the total increase in turnout was only 24 percent.

The challenge to Sen. Ted Cruz has Republicans in Texas (and beyond) concerned, with a 16 percent uptick in GOP turnout versus an 88 percent increase for Democrats. But with Dems only taking a 40 percent vote share amid a 37 percent overall increase, Beto O’Rourke’s turnout might be more threatening to the state’s two vulnerable congressmen.

Similarly, in Arizona, the wild senate primary only boosted GOP turnout 22 percent to the Democrats’ 65 percent. But the GOP’s majority vote share suggests the state’s Republican lean could yet carry the day for Martha McSally.

In Colorado, which has an open governorship and a toss-up House seat, overall turnout spiked 90 percent, led by a 198 percent Democratic increase to a 56 percent vote share. In Nevada, however, the 88 percent Democratic increase produced a bare 51 percent vote share, leaving hope for Republican Sen. Dean Heller.

On the West Coast, California’s “top two” primary system confuses matters, but an 82 percent rise in Democratic turnout and 65 percent vote share helps explain why the GOP remains nervous about six House seats, despite a 46 percent increase in Republican turnout. In Washington state, the 76 percent spike in Democratic turnout (versus a 12 percent GOP uptick) has raised concerns regarding three potentially vulnerable House seats.

In short, the pattern in primary turnout is clear. In state after state, Democrats have been swarming the polls and swamping GOP turnout increases. Conservative-leaning voters may be dismissing the potential blue wave as “fake news” in focus groups, but they would be better off warning their family, friends and neighbors to avoid a worst-case scenario, especially for the House.