There's a lot of talk these days about how a Democratic wave may be building for the 2018 midterm elections. Usually this wave is discussed in terms of Democrats having a shot at ousting Republicans in the U.S. House and maybe the U.S. Senate. But could a Democratic wave form in gubernatorial races, too?

Logically, an energized Democratic voter base, like the one seemingly developing this year, should give the party's candidates a leg up in any race on the ballot. But state races, such as those for governor, are more likely than federal races to revolve around state-level issues and the individual personalities and records of the nominees. In other words, they seem more likely to break with up-ballot trends.

So we took a closer look at the recent history of wave elections to analyze the connection between a national wave and state elections. We looked at the most recent three wave elections: 2006, which benefited the Democrats, and 2010 and 2014, which benefited the Republicans. These also happen to be the last three midterm elections; if a wave develops again in 2018, it would be the fourth midterm wave in a row.

Here's the rundown of what happened:

Year President and Party U.S. House Seats Lost by President's Party U.S. Senate Seats Lost by President's Party Governor Seats Lost by President's Party 2006 Bush, R 30 6 6 2010 Obama, D 63 6 6 2014 Obama, D 13 9 3

In each case, the president's party experienced double-digit losses in U.S. House seats and the loss of between six and nine seats in the U.S. Senate. In the meantime, the president's party lost between three and six gubernatorial seats -- a pretty significant fraction of the 36 gubernatorial races typically on the ballot during midterm elections.

This data suggests there's a correlation between a congressional wave and gubernatorial gains. But we decided to dig deeper.

We looked back at this column's final pre-election gubernatorial handicapping in each of the wave elections to see if there was any consistent pattern in the number of races that were actually considered competitive going into Election Day and that the president's party ultimately lost. We consider contests competitive if we rate them "tossup," "lean Democratic" or "lean Republican."

Here's the rundown:

Year Total Competitive Seats D-held Competitive Seats R-held Competitive Seats D-held Open Seats R-held Open Seats Governor Seat Shift in Election 2006 18 6 12 1 9 D +6 2010 18 8 9 4 8 R +6 2014 18 9 9 5 2 R +3 2018 17 5 12 3 7 TBD

One thing that leaps out of this comparison is how consistent the number of competitive races has been during wave elections -- almost exactly half the 36 races in each election.

Another notable finding is that the 2018 gubernatorial landscape seems to resemble the last Democratic wave year in 2006. The ratio of Republican-held competitive seats to Democratic-held competitive seats was about two-to-one. And the ratio of open gubernatorial seats -- which are typically easier to flip due to the lack of an incumbent running -- also tilted heavily in the Democrats' favor in 2006. At this point, at least, 2018 is looking to shape up the same way.

The Republican wave years of 2010 and 2014 displayed a more mixed pattern -- in 2014, the Democrats had to defend more open seats, but in 2010, it was the Republicans who had to defend more open seats.

My guess about why 2010 showed an atypical pattern: In the 2002 midterms, there were a lot of unexpected results because voters in many states were suffering through a recession-linked budget crisis and lashed out at the party in power. That left an unusually large number of Democratic governors in red states and Republican governors in blue states. Many of those governors managed to win a second term in 2006, but most were term-limited out in 2010. So there were a lot of open seats in 2010 where the minority party actually had a leg up going into the election.

All this data suggests, first, that gubernatorial elections have been subject to the same forces as congressional seats during a wave election, and second, that the conditions for competitive seats and open seats in 2018 are broadly in line with previous wave elections that produced net gains of three to six gubernatorial seats for the minority party.

To make sure this was more than a coincidence, we looked next at the individual contests in each of the past wave elections. We checked with experts in those states to see if they recalled the national wave being a factor in determining the winner. In each of the three cycles, we found between six and 10 seats that may have been influenced by the wave.

One of those states was Maine, where Republican Paul LePage won in both 2010 and 2014. In both cases, he was aided by the presence of a third-party candidate, but his aggressively conservative message jibed with the Republican mood both years. "He ran as a conservative in a state of fairly liberal politics, and he explicitly ran against the state legislature -- long held by Democrats -- and some of their policies," says Kenneth T. Palmer, an emeritus political science professor at the University of Maine.

In Massachusetts in 2014, Republican Charlie Baker flipped a Democratic open seat, in part due to a weak Democratic candidate, Martha Coakley. Still, "it's likely that the trend toward Republicans nationally helped Baker," says Tufts University political scientist Jeffrey Berry.

In other states, the impact of a wave was even clearer.

In Iowa in 2006, for instance, Democrat Chet Culver pulled off something of an upset victory due in large part to the declining popularity of the Bush administration, says University of Northern Iowa political scientist Christopher Larimer. The script reversed four years later, when Culver lost by nearly the same margin. The Tea Party wave and dissatisfaction with President Barack Obama and his health-care bill certainly helped former GOP Gov. Terry Branstad win, Larimer says.

Much the same pattern played out in Michigan, says Bill Ballenger, who publishes The Ballenger Report, a Michigan political tipsheet. "2006 in Michigan was what it was nationally -- a blue wave with an anti-Bush backlash," he says. "2010 was just the opposite, a huge red wave that helped Republican Rick Snyder win the governorship by about 18 points."

In Ohio in 2010, Republican John Kasich was able to oust first-term Democratic Gov. Ted Strickland thanks in part to the GOP wave. "Strickland did not raise taxes and had no major scandals," says Bill Binning, a former Republican Party official. "He was moderate and from Appalachia, so there was little reason for him to lose beyond the wave."

In closely divided Florida, the Republican waves of 2010 and 2014 played a key role in Republican Rick Scott's two narrow victories. "Scott was unknown and unpopular in 2010 and very unpopular in 2014, but he won narrowly in both elections because of the Republican wave," says Steven Tauber, a University of South Florida political scientist.

Then there's Kansas, where Republican Gov. Sam Brownback -- who was facing a well-funded Democrat and who endured boos on the campaign trail -- won a second term thanks to the 2014 GOP wave. Well-funded outside groups effectively nationalized the political atmosphere in Kansas, including the gubernatorial race, successfully linking the Democratic nominee, Paul Davis, to Obama and the national Democratic Party.

"Brownback should have lost in 2014, was supposed to lose in 2014, and by the look on his face when he walked into his victory party, was shocked he didn't lose in 2014," says Washburn University political scientist Bob Beatty.