Analysis: The math behind Democrats' quest to win Pennsylvania special election

For the past five months, Democrats and Republicans alike have been pouring money into the next special election that takes place Tuesday in Pennsylvania’s 18th Congressional district.

Feeling bullish after big wins in other special elections last year and enjoying a groundswell of grassroots activism these days, Democrats are hoping a win in this ruby red district will not only make it easier for them to take back the House in November, but also send a message that their candidates can play in any part of the country.

But while both sides have decided that the race is worth digging deep into their pocketbooks, the fact remains that, unlike Virginia and part of Georgia where candidates also went head to head last year, this area in Pennsylvania voted solidly and overwhelmingly Republican in 2016.

According to our ABC News analysis, Democrat Conor Lamb would need to pull off an electorate trifecta of sorts to win the race, by greatly increasing the Democrat turnout over what it would typically be in a midterm or special election, convincing moderate or swing voters to go blue and lucking out with depressed Republican turnout.

President Donald Trump won this area by 20 points in 2016, and even in the most heavily Democratic precincts in the district right around Pittsburgh, former Secretary of State Hillary Clinton only won on average 56 percent of the vote. By comparison, nearly half of the total votes cast in the district in 2016, came from precincts where president Trump won by over 30 percentage points.

If the rest of the 2016 Clinton-Trump modeling performance stayed the same and if, for example, Lamb was able to bring out his own wave of Democratic voters and increase the number of votes in the most heavily Democratic precincts so those areas made up 10 percentage points more of total vote as compared to in 2016, that still would only get him within 15 percent of Republican Rick Saccone in the special election.

Likewise, if Lamb outperformed Clinton in the most heavily Democratic areas and most Republican areas, and, for the purposes of debate, took 72 percent of the vote in the bluest areas where Clinton only took 56 percent and 41 percent in the reddest areas where Clinton only took 26 percent, that would still only get Lamb within nine points.

State Rep. Greg Rothman serves with Sacconne in the Pennsylvania legislature and worked on the team that helped Trump win in the state. According to Rothman and other experts from the area, union, blue-collar workers who traditionally voted as conservative Democrats made all the difference in a securing the president’s win in the area.

Rothman told ABC News he thinks those same voters are excited to vote for Saccone.

He said if turnout was high that would “absolutely” be good for Saccone.

“The reality is it is a safe Republican seat, and I believe people will show up to vote for the guy they know and for Donald Trump’s agenda because they like what is happening,” he said.

In order to make up the 20 point differential from 2016, Lamb would likely need to outperform Clinton in almost every type of district, not only doing better than Clinton did against Trump in the bluest areas but also doing significantly better in the reddest areas and breaking near even with the Republican in the more moderate, average parts of the district where Trump in 2016 won by around 20-21 points.

Lamb’s best shot at eeking out a victory will be if he increases the turnout in the bluest areas, wins a higher percentage of the bluest areas and also swings folks in the reddest parts of the district.

One hypothetical model that puts Lamb just over 50 percent, includes, for example, him increasing the percentage of the vote that comes from the bluest areas by nine points, winning four percent more of the vote than Clinton did in those bluest areas, breaking even with Saccone in areas in the district Trump won by 21 points and, in the reddest areas were Trump won by 46 percent, only losing to Saccone by about 15.

Democrats in Washington, D.C. told ABC News they think Lamb has benefited from the Republican tax plan, which they argue is a "handout to the rich and largest corporations at the expense of the middle-class families."

"John McCain, Mitt Romney, and Donald Trump all won Pennsylvania’s 18th district by at least 15 points, so the fact that this race is neck-and-neck clarifies that this tax scam is a political liability. The scary thing for vulnerable House Republicans this year is that neither the National Republican Congressional Committee nor [aligned super PAC] seem to have any clue what to do about it," Tyler Law, spokesperson for the Democratic Congressional Campaign Committee told ABC News in an email.

Saccone, has received nearly $10.3 million support from super PACs and outside groups, including $3.3 million from the House-aligned super-PAC called the Congressional Leadership Fund and $3.5 million from the official election arm of the House Republican conference. Typically, groups like these do not spend so heavily unless they are worried about retaining the seat.

Had they calculated the seat was safe or a lost cause, they likely would have scaled back their spending.

On the other side of the aisle, Lamb has raised nearly $3.5 million since January for his campaign directly, and outside groups backing him have spent only about $1.7 million in the race so far.

WATCH LIVE TONIGHT: You can watch livestreaming coverage of Pennsylvania’s special election as part of ABC News’ “18 for 18” coverage of the midterm elections starting at 8 p.m. ET on ABCNews.com or on the ABC News app available on the Apple App Store, GooglePlay Store, Apple TV App Store, and Roku Channel Store. Don’t forget to sign up for Midterm Elections Alerts to get more coverage of this year’s election season as par from our powerhouse politics team.