Washington (CNN) Today, voters in southwestern Pennsylvania will head to the polls to choose their new member of Congress. The fight between state Rep. Rick Saccone (R) and veteran Conor Lamb (D) was never expected to be close given that President Donald Trump won the 18th District by 20 points in 2016.

But Saccone has struggled as a candidate and a fundraiser while Lamb has shined. And Trump's struggles in his first year in office have emboldened Democrats in the district to use the special election as a way to send a message to the President. Polling conducted in the final days of the race suggest Lamb is the slight favorite to pull off an upset that would carry with it massive national implications.

To better understand the race -- and what it all means about and for Trump -- I reached out to Jon Delano , the lead political analyst for Pittsburgh's KDKA, for his perspective. Our conversation, conducted via email and lightly edited for flow, is below.

Cillizza: Everyone agrees the race is close. No one agrees why. Is this mostly about Trump? Saccone? Lamb? Murphy?

Delano: In a district that Donald Trump won by nearly 20 points and no Democrat has come close to winning in decades, it's undeniable, in my view, that this election is a referendum on the performance of President Trump.

On the ground, it's been a coalition of anti-Trump groups, many that sprouted after Trump's election and led by women, that have been the volunteer backbone of the Lamb campaign.

It is also true that Lamb has run a solid campaign, unifying Democrats, especially union Democrats, many of whom had backed the former Republican incumbent Tim Murphy, who often tossed votes to the trade unions. Saccone has a record in the state legislature of opposing organized labor on just about everything, and that has helped Lamb with many union members.

But, fundamentally, as the President's visit to Pittsburgh on Saturday reinforced, if you like Trump, you vote Saccone, and if you don't, you back Lamb.

Cillizza: Where did Lamb come from? This is a district where Democrats didn't even field a candidate against Murphy in 2014 or 2016.

Delano: Conor Lamb comes from a Democratic political family with deep roots in Allegheny County politics. His grandfather was a state senator who served as majority leader when the Democrats controlled that body in the 1970s. Conor's uncle was elected twice as city controller in Pittsburgh. Conor's father worked in the Congress in the 1980s for US Rep. Austin Murphy, and is now a well-connected top government affairs officer for PNC, the nation's ninth largest bank.

In short, Lamb has politics in his blood. Because there is no primary to pick nominees in special congressional elections, it's essentially an insider's game. Lamb's family connections and resume (assistant US Attorney & former Marine lawyer) with no record to hurt him positioned him to win on the second ballot among the 554 Democratic committee people in the four counties who voted.

Ironically, in that vote, he positioned himself as slightly more liberal, defeating Westmoreland County commissioner Gina Cerilli who describes herself as a pro-life, pro-gun, and pro-union Democrat.

As to why no Democrat challenged US Rep. Tim Murphy in 2014 and 2016, that's easy. Murphy was the hardest-working congressman this region has seen in a long time, attending every imaginable event (to the detriment of his home life) and positioning himself as a moderate-to-conservative representative on all the key issues.

Cillizza: Did Republicans make a mistake in picking Saccone, an older longtime state legislator? Were there other possible candidates who could have been a better fit?

Delano: Like the Democrats, the Republicans do not have a primary to select their nominee in a special congressional election. They use a conferee process whereby the Republican chairs of the four county parties pick individuals to vote for a nominee.

On the first ballot, the 215 conferees split their votes with 75 for state Sen. Guy Reschenthaler, 74 for Saccone, and 66 for state Sen. Kim Ward. On the second ballot, Ward threw her support to Saccone, and he won handily.

Ironically, Reschenthaler would have looked a lot more like Lamb. An energetic, 34-year-old US Navy veteran who, like Lamb, had served as a military lawyer, Reschenthaler also, unlike Lamb, has legislative experience as a state senator. His loss to Saccone has created some bitterness in the GOP. But with the party inclined to support the more pro-Trump candidate, Saccone -- who told me over a year ago that he was Trump before Trump -- was the obvious favorite. Privately, some Republican insiders say if the party had picked Reschenthaler, Lamb would have had no shot at winning. Who knows.

Cillizza: National conservative groups have run a slew of ads trying to link Lamb to Nancy Pelosi. Do you see evidence it's working?

Delano: It is true that many voters in western Pennsylvania do not like Nancy Pelosi. It is easy to characterize her as one of those "coastal liberals" that seem to dominate the Democratic Party. But I don't see yet that the national Republican efforts to link Lamb to Pelosi is working. That's especially true since Lamb has been clear that he will not vote for Pelosi as leader. Of course, if he loses, the Pelosi connection will be validated in the eyes of some. In general, the outside PAC attack on Lamb has struck many as so over-the-edge as to be unbelievable. But, again, let's see who wins before we declare it was ineffective.

Cillizza: "Finish this sentence: "If Conor Lamb wins on Tuesday, it will tell us _____________ about the 2018 midterms." Now, explain.

Delano: "If Conor Lamb wins on Tuesday, it will tell us that even in solid Trump country, the right kind of Democrat can win in the 2018 midterms."

Of course, the President and Republicans will blame Saccone for the loss and distance themselves from the campaign. On Monday, Donald Trump Jr. told me that this election was NOT a referendum on his father's performance in the White House. But if Saccone wins, I suspect we will hear something different. While the old adage -- all politics is local -- is generally true, in my view, President Trump has nationalized the 2018 midterms. As a close observer here in western Pennsylvania, it's clear to me that the passion is on the side of the anti-Trump voters who intend to send a message by electing Conor Lamb. We will know shortly if that is enough to win.