Let's start by saying this: It is a looooong shot for Democrats to take back control of the House of Representatives this November.

Democrats would need effectively run the table of competitive seats as judged by non-partisan political handicappers.

But we'll also say this: What was once thought to be pretty much impossible could now be within the realm of possibility. And there could be a specific way to measure whether such a once-fanciful dream for Democrats could come true: The percentage of the vote the Democratic presidential nominee gets in November.

For reasons we'll get into below, Kyle Kondik and Geoffrey Skelley of the University of Virginia's Center for Politics think that number is 54 percent. And for reasons we'll get into below, that number's a long shot, too. It'd be the highest percentage a winning presidential candidate has received in two decades.

Let's back up for a minute and explain why the House could be in play this November. It's all thanks to the guys Republicans appear to be on their way to nominating for president: either Donald Trump or Ted Cruz.

Nonpartisan analysts who study this kind of thing for a living think either a Trump or Cruz nomination would be untenable for so many Americans that it could knock off Republicans further down the ticket -- perhaps enough to give Democrats the 30 seats they need to win the majority. (The current breakdown in the House is 246 Republicans to 188 Democrats.)

The simplest explanation for that phenomenon is that people who come out to vote for the Democratic nominee are simply more likely than not to just check the ballot for Democrats all the way down.  If enough Democrats come out and enough Republicans don't, lots and lots of Democrats win.

The top 10 House seats most likely to flip in 2016

So what is "enough"? Well, in 2012, President Obama won almost exactly 52 percent of the vote.* That, as you'll recall, was not enough of a wave to swing the House in his direction; Republicans picked up a net 13 seats.

Using the 2012 election and its effect on down-ballot races as a baseline, Kondik and Skelley crunched the numbers and found that Hillary Clinton (or Bernie Sanders) would have to get 54 percent of the vote in November to give Democrats a shot at winning the House. Such a high turnout on their side would essentially give Democrats a chance to net 35 House seats, which is five more than they need to get the majority.

Upping Obama's victory by two points might sound relatively doable -- it's not 10 points, for example. But it's not all that easy, for a few reasons:

  • Two points is a lot for a presidential candidate to scrape together in our highly polarized nation. As Kondik and Skelley point out, it's several points more than any presidential winner has gotten this century. Not since Clinton's husband, Bill Clinton, won in 1996 with 54.7 percent of the vote has a candidate received 54 percent (even Obama's historic 2008 win earned him 53.7 percent). What's more, for the past seven presidential elections, neither candidate has gotten more than 55 percent of the vote.
  • Clinton, who is the party's most likely nominee, doesn't seem to be the one to break that historical pattern. She's not well-liked in some critical swing states, like in Pennsylvania, where a recent Quinnipiac poll shows 59 percent of voters view her unfavorably, while just 35 percent view her favorably.  In 2008, 65 percent of Pennsylvania voters liked Obama, according to a Marist poll taken a month before the election. It's just one state, but those numbers suggest Clinton has a lot of ground to make up -- and then some -- if she's going to win by more than Obama did in 2008.
  • There's also early evidence that Republican voters who want an outsider for president (aka Trump and Cruz) are fine sending an incumbent back to Congress to work with him. So far, all incumbent Republicans who have been challenged by someone from their own party have won those primaries.
  • And then there's the wildcard factor, which is that no one really knows what's going to happen this election. If you would have told us a year ago that we'd be writing a story about Democrats' potential for erasing Republicans' majority in the House, we'd probably laugh. As Republicans like to say, the last time their party held a bigger majority in the House, Babe Ruth was playing for the Yankees. It just didn't seem within Democrats' reach anytime this decade.

But if there's one thing this election has taught us, it's that the old rules may no longer apply. And that's the biggest caveat of all. All of this is really an educated guess -- by very smart people, no doubt, but just a guess. We're trying to use the old rules to interpret the new. Which means seven months  from now, we might be laughing at this article's predictions, too.

*For the purpose of determining which party controls congressional seats, we and the University of Virginia are measuring all vote totals as between the two major parties. So among Democratic and Republican voters, Obama got almost 52 percent of the vote, and Hillary Clinton would have to get 54 percent of the two-party vote. The number changes when you add in non-major party voters, like independents, etc.