Discussion of an impending "blue wave" has proliferated throughout the political landscape since November 2017, aided in part by the media and a Democratic Party eager to claw its way back into power.

Yet very little evidence or research exists on what exactly constitutes a wave election or how they can be measured in the future. A new analysis by Ballotpedia attempts to break ground on the subject by examining data from 50 previous election cycles, ranging from 1918 to 2016, in order to appropriately determine how many seats Democrats would need to win in 2018 for their "blue wave" to not only crest but reach the shore.

Ballotpedia's analysis defines a "wave" as 20 percent of elections in the last 100 years, in which the president's party lost the most seats. Using this definition, Ballotpedia measured prior political performance to determine Democrats would need to win at least 48 House seats, 7 Senate seats, 7 gubernatorial seats, and 494 state legislative seats for 2018 to be counted as a wave election.

If that sounds like a large hurdle for any party to overcome, let alone one which has struggled with fundraising, messaging, and bridging ideological divides, that's because it is.

Robert Oldham, a staff writer on Ballotpedia's Marquee Team and one of the report's authors, told the Washington Free Beacon there is a reason why wave elections are not a frequent occurrence in American politics.

"We were working from the idea that if waves can be defined, and that's a big if, they should be significant and relatively rare historical events," Oldham said. "We looked at the last 100 years of election data and found that 1 in 5 elections [can be deemed] waves."

The report also found wave elections are often not synonymous across all levels of government. After examining the 50 elections since 1918, the authors found there were 11 wave elections in the House where the president's party lost 48 or more seats, and only 10 waves in the Senate resulting in a loss of 7 or more seats by the party in power. Of those elections, six occurred in the House during a president's first midterm election, while there were only three in the Senate.

On paper, at least, the coming 2018 midterm elections seem to favor the Democratic Party.

A mass exodus by incumbent House Republicans, who are either retiring outright or seeking higher office, has endangered the chamber's 23-seat majority. The retirements, numbering 60 as of June, have disproportionately impacted Republicans, forcing the party to defend 50 open seats this cycle, compared to 20 for the Democrats.

Any upper hand Democrats might hold in the House, however, is compounded by challenges posed in the Senate, where the party is forced to defend 25 out of the 33 seats up for election. As the report notes, 10 of those seats are in states like North Dakota, Missouri, and West Virginia, where President Trump won by double digits.

Oldham stated it is difficult to conceptualize a wave election taking place in 2018, at least using the definition developed by Ballotpedia.

"Based off the number of battlegrounds, Democrats would need to win every single seat up to make it into the top 20 percentile for wave elections," Oldham said. "That's incredibly difficult to do."

Complicating matters further is that polling, an initial indicator of electoral trends and outcomes, has begun to turn against the Democratic Party.

The party's advantage on the generic congressional ballot has shrunk from a high of 18 points in December 2017 to 4-to-6 points as of June 2018. Many have been quick to dismiss the dwindling lead, pointing to flaws existing on the generic ballot poll that measures party preference via a national survey rather than a district-by-district approach while paying little attention to the generic ballot's tendency to exaggerate the Democratic vote.

Perhaps more telling, the Democrat's rapidly disappearing advantage on the generic ballot has coincided with accelerated job growth, consumer confidence nearing an 18-year high, and job market optimism hitting the highest point ever recorded.

Adding to the mix is the sharp rebound in President Trump's approval rating. In January 2018, according to Gallup, Trump's approval rating stood at a dismal 37 percent. By June, however, it had climbed 8 points to 45 percent, with some polls even showing a 10-point jump to 47 percent.

The substantial improvement is unprecedented compared with the standings of Presidents Bill Clinton, George W. Bush, and Barack Obama heading into the midterm elections of 1994, 2006, and 2010. Rather than gaining ground, such as Trump, all three presidents witnessed their approval ratings plummet, in some cases by double digits, resulting in their parties suffering rebuke at the ballot box.

In January 1994, Clinton's approval rating was at 54 percent. By June of that year it had fallen 10-points to 44 percent and hit a low of 41 percent by mid-October, resulting in Democrats losing 54 House seats that election cycle. A similar scenario repeated itself in 2006—Bush's approval rating fell six points between January and mid-October. In 2010 Obama's approval dropped by seven points.

One factor that Ballotpedia's report could not adequately account for was existing limitations in the electoral system such as redistricting.

The authors found that following the 2010 elections, Republicans controlled the redistricting process in states making up nearly 40 percent of the U.S. House. Democrats, meanwhile, controlled the process in states composing only 10 percent of the chamber.

"If Republicans redrew the lines to benefit their candidates, then it might lower the threshold for a Democratic wave because seats will be more difficult to win than under Democratic-controlled redistricting," the authors wrote in their analysis.

A similar sentiment was echoed by Dave Wasserman of the Cook Political Report in August 2017. Wasserman found redistricting had resulted in House seats leaning towards the GOP at levels unseen since 1920. He reached a similar conclusion when examining the 2018 Senate map.

All of this throws cold water on the conventional wisdom of a coming "blue wave."

"The thresholds for what Democrats would have to meet for 2018 to be considered a wave election are incredibly high," Oldham said.