PITTSBURGH (KDKA) — Western Pennsylvania continues to be an important focus in the 2020 presidential election.

The Pennsylvania primary is April 28, meaning that it’s unlikely Pennsylvania’s Democrats will choose the nominee directly.

But presidential candidates have already started coming here, including former Vice President Joe Biden and U.S. Sen. Bernie Sanders. President Donald Trump’s recent visit to the Shell plant in Beaver County certainly had a campaign-like feel.

Candidates know that Pennsylvania is one of the must-win states to win the White House in 2020.

Only two Republicans have ever won the presidency without carrying Pennsylvania — Richard Nixon and George W. Bush.

And no Democrat has won the White House without Pennsylvania since Harry Truman in 1948.

On Wednesday, U.S. Senator Amy Klobuchar, a Minnesota Democrat, brought her campaign to Pittsburgh.

Photo Credit: KDKA

Klobuchar, a self-styled Midwestern moderate, toured the Carpenters Training Center in Collier and held a campaign meet-and-greet event for about 300 supporters in Oakland.

In an interview with KDKA’s Jon Delano, Klobuchar said that this region cannot be “fly-over” country for any successful presidential candidate.

How a Democrat wins this region is another matter, as Donald Trump carried every county in Western PA except Allegheny in 2016.

Klobuchar told KDKA’s Jon Delano, on issues of energy, she has never called for an immediate ban on fracking or a day-one shut-down in fossil fuels, as some have.

She favors “green energy” alternatives but said achieving that requires a “common-sense” approach.

On trade issues, Klobuchar said she’s been “tough” on China, especially when it comes to steel, and she relates to this region’s trade issues because of similar issues involving iron ore in Northern Minnesota.

While Klobuchar was visiting in person, Mayor Pete Buttigieg, the mayor of South Bend, Indiana, announced a list of 50 mayors nationwide who endorsed his candidacy.

WATCH: KDKA’s Jon Delano interviews Monessen Mayor Matt Shorraw.

Among them was Mayor Matt Shorraw, the 28-year old mayor of Monessen, a city of 7,700 in Westmoreland County.

In 2017, Shorraw defeated the incumbent Mayor Lou Mavrakis, a fellow Democrat who endorsed Donald Trump and invited him to Monessen in the 2016 campaign.

Trump campaigned in Monessen and carried much of the area, although he did lose Monessen.

Shorraw told KDKA’s Jon Delano that he endorsed Buttigieg — whom he has not met in person yet — because the Midwestern mayor understood the issues that impact small towns like Monessen. And, of course, he’s invited Buttigieg to Monessen.

With the Iowa caucus and New Hampshire primary are less than 20 weeks away, it’s unclear how many other candidates will focus on Pittsburgh this fall.

But don’t be surprised if a few more test their potential strength in a region that will be key to winning Pennsylvania in November of 2020.