As the nation heads into a midterm election in which some three dozen states will vote for governor, it's a good time to remember just how important finding the right gubernatorial candidate can be for a party's chances statewide.

Getting stuck with a weak gubernatorial candidate doesn't mean simply ceding the governor's race. It also impacts fundraising, media attention and, even more important, turnout on Election Day. In other words, a weak candidate hurts down-ballot candidates too.

As evidence, look no further than Nevada in 2014.

That year, the incumbent Republican governor, Brian Sandoval, was so popular that the strongest Democratic candidates took a pass on the governor's race. As a result, the party ended up with Robert Goodman, a septuagenarian political novice who had headed the state's tourism and economic development department in the 1970s.

How obscure was Goodman? In the Democratic primary, he won 25 percent of the vote. However, that was less than "none of these candidates," which is a ballot option in Nevada and secured 30 percent of the Democratic primary vote.

To make matters worse, the state's Democratic powerbroker, then-U.S. Sen. Harry Reid, announced roughly three months before the general election that he would not be spending time or money to help Goodman.

Sandoval ultimately defeated Goodman, 71 percent to 24 percent. Goodman's raw vote total of 130,722 was less than half of the 298,171 the 2010 Democratic candidate, Rory Reid (Harry's son) received. That's 167,000 fewer Democratic votes from one election to the next. And it wasn't as if these Democratic voters shifted to Sandoval; the incumbent's haul of raw votes rose by only 4,000 or so between 2010 and 2014.

Now, it's true that 2014 was a rough midterm election for Democrats everywhere. But their down-ballot performance was particularly poor in Nevada, especially given the quality of their candidates. Let's recap, race by race:

In the attorney general contest, Democrat Ross Miller, the secretary of state and son of a former governor, lost an open-seat race to Republican Adam Laxalt, the grandson of a former governor and senator.

Laxalt got almost exactly the same number of votes as the losing Republican candidate in 2010, Travis Barrick. But whereas Barrick lost in a rout to Democratic incumbent and now U.S. Sen. Catherine Cortez Masto, the 2014 Republican vote haul was enough to elect Laxalt attorney general. That's because the number of raw votes for the Democratic AG candidate cratered by 34 percent between 2010 and 2014.

What about Miller's previous office, secretary of state? In 2014, Republican Barbara Cegavske only improved upon the raw-vote performance of the 2010 Republican candidate by about 4 percent. Yet that was enough to defeat Democrat Kate Marshall, because Marshall's vote total crashed by 33 percent compared to Miller's four years earlier.

The worst numbers came in the race for lieutenant governor. The percentage of raw votes for Republican Mark Hutchison in 2014 fell by 10 percent compared to the winning 2010 candidate, Republican incumbent Brian Krolicki. But Democrat Lucy Flores underperformed 2010's Democratic candidate, Jessica Sferrazza, in votes by 38 percent. The Democratic decline was enough to give Hutchison a sweeping victory.

"In 2014, the Democrats […] lost every constitutional office and both houses of the Legislature as well as two congressional seats," says Jon Ralston, who publishes the Nevada Independent. He adds, "It's generally better to have strong top of ticket."

Nevada is far from a one-off example.

Consider Ohio's 2014 elections. Republican John Kasich won his first gubernatorial term in 2010 and was expected to get a tough challenge for re-election from Cuyahoga County Executive Ed FitzGerald. Thanks to a sex scandal, that never happened. "The Democratic base was depressed by the FitzGerald scandal, and their enthusiasm waned," says Mark R. Weaver, a veteran GOP strategist in Ohio.

Kasich's raw vote totals rose slightly between 2010 and 2014, by about 55,000 votes. But his opponent, FitzGerald, ended up getting 44 percent fewer votes than the 2010 Democratic candidate, incumbent Gov. Ted Strickland. A whopping 802,000 Democratic votes at the top of the ticket simply vanished.

The poor showing rippled down-ballot. In the attorney general race, incumbent Republican Mike DeWine increased his raw vote total by about 3 percent between 2010 and 2014. The number of Democratic votes in those two races fell by 34 percent. What had been a close race for AG in 2010 became a 23-percentage-point rout.

And in Ohio's secretary of state race, Republican Jon Husted saw his own raw vote total decline by 10 percent between 2010 and 2014, but the Democratic candidate's showing slumped even more dramatically, with her raw vote shrinking by 31 percent.

Of course, Democrats haven't been the only ones to suffer down-ballot from a weak gubernatorial candidate.

In 2014, incumbent Democratic California Gov. Jerry Brown faced Republican Neel Kashkari, who had served in the George W. Bush Treasury Department. Kashkari had little to no experience in electoral politics, so Brown and the media paid him little notice. On Election Day, Brown won 60 percent to 40 percent. The Democratic incumbent received 19 percent fewer raw votes than he had in 2010, but Kashkari underperformed the previous Republican candidate's raw vote total by 29 percent.

Kashkari's weak top-of-the-ticket performance hurt one down-ballot race. In the 2010 open-seat race for attorney general, Democrat Kamala Harris barely defeated Republican Steve Cooley, winning by less than a percentage point. In 2014, she won 8 percent fewer votes than she had four years earlier, yet the 2014 Republican nominee, Robert Gold, saw his vote total collapse by 31 percent compared to Cooley. (Kashkari's effect was much weaker in the races for California's lieutenant governor and insurance commissioner.)

Meanwhile, there are many states where one party has been unsuccessful for so long that their bench lacks strong candidates of any kind.

In Nebraska, for instance, the electorate is so overwhelmingly Republican that "it's challenging for Democrats in races at most every level," says John Hibbing, a University of Nebraska political scientist. "In the last gubernatorial race, the Democrats actually had a very strong candidate, Chuck Hassebrook. He had experience, name recognition, some money and many contacts in the important rural parts of the state. Yet he was clobbered, as were many down-ballot Democrats."

To Hibbing, though, the problem for Nebraska Democrats has less to do with recruiting a gubernatorial candidate than having to run "an uphill battle in terms of partisan dynamics" in essentially every race.

In another solidly Republican state, Tennessee, political scientist Anthony Nownes says it's been a while since the Democrats have offered a well-known, well-funded gubernatorial candidate. "So I am not sure what the down-ballot races would look like if they did," he says.

As the 2018 gubernatorial elections inch closer, the challenge of recruiting a strong candidate -- and hoping that favored candidate survives a primary -- is troubling party strategists.

In Arkansas, for example, the Democrats "are starting to collect some decent candidates for down-ticket races, but there's no real sign of a legitimate opponent against Republican Gov. Asa Hutchinson," says Jay Barth, a political scientist at Hendrix College. He adds that failing to find a strong gubernatorial candidate could cost Democrats "five or six points -- enough to definitely matter."