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WATCH: Trump pushes tax law in Pennsylvania as special election approaches

UPDATE: President Donald Trump is promising to return to Pennsylvania to campaign for a state lawmaker who’s vying to keep a U.S. House seat in the Republican column.

Trump says the candidate, Rick Saccone, is a “great guy” and a “special person.”

Says Trump: “I’ll be back for Rick.” He promised to fill a stadium for Saccone, which suggests Trump may return for a campaign rally.

Saccone is running for the seat that opened up when the incumbent, GOP Rep. Tim Murphy, resigned after admitting to an extramarital affair.

Saccone faces Democrat Conor Lamb, a former Marine, in the March 13th special election

3:05 p.m.:

President Donald Trump on Thursday pledged “total support” for a Pennsylvania lawmaker trying to keep a House seat in Republican hands in the first congressional race of the year, tweeting his endorsement hours before visiting the state.

However, the White House later corrected Trump’s tweet to say the president was traveling to Pennsylvania to promote his tax overhaul, not to campaign for Rick Saccone.

Trump tweeted early Thursday that Rick Saccone “is a great guy” and said, “We need more Republicans to continue our already successful agenda!” The 59-year-old state representative faces Conor Lamb, a 33-year-old lawyer and former Marine, in the March 13 special election as Democrats look to build on their Senate victory in conservative Alabama and lay the groundwork for gains in the midterm contests in November.

The president’s official mission during the trip to the Pittsburgh area was to praise recently enacted GOP tax cuts. Trump planned to appear with Saccone, though the White House had said the president wouldn’t be mentioning the candidate in his remarks. Trump was traveling to the 18th Congressional District, where GOP incumbent Rep. Tim Murphy resigned after admitting to an extramarital affair.

The election is shaping up as the next test of Democratic enthusiasm and GOP resilience in the Trump era and an early indicator of whether a midterm wave may be coming in November, as Democrats hope. They want to want to show they can win in Trump territory without benefit of a scandal or flawed candidate, as was the case with Republican Roy Moore in the Alabama Senate election.

“Will be going to Pennsylvania today in order to give my total support to RICK SACCONE,” Trump tweeted.

Saccone, in an interview Wednesday, framed his candidacy as an extension of the agenda that propelled Trump. “It’s only natural to have him come out to see his core constituency and have us celebrate his successes with him,” Saccone said.

The election is shaping up as the next test of Democratic enthusiasm and GOP resilience in the Trump era and an early indicator of whether a midterm wave may be coming in November, as Democrats hope.

The White House would confirm only that Saccone was to greet the president at the airport and attend Trump’s tour of a factory. Later Thursday, press secretary Sarah Sanders sent out a statement correcting Trump’s tweet.

“While the president has made clear his support for Republican candidates throughout the country, including in Pennsylvania, the purpose of today’s visit is to promote the president’s successful agenda especially on taxes,” she said.

Trump’s visit to the H&K Equipment Company in Coraopolis, Pennsylvania, has been billed as an official event, rather than a campaign stop. A campaign event would require that taxpayers be reimbursed for some of the expenses.

Saccone, a retired Air Force officer with a doctorate in international affairs and experience in counterterrorism, said he didn’t know whether he would sit with the president or even get to spend any one-on-one time with him. “I don’t have any details,” he said after spending the day in Washington raising money with GOP House leaders.

This stream is provided by the White House. PBS NewsHour will update this story as it develops.