CORAOPOLIS, Pa. (Reuters) - President Donald Trump traveled to western Pennsylvania on Thursday to show his backing for the Republican candidate in a special congressional election where Democrats are hoping to score another upset victory in Trump-friendly territory.

U.S. President Donald Trump shakes hands with special election Republican candidate Rick Saccone upon his arrival in Pittsburgh, Pennsylvania, January 18, 2018. REUTERS/Kevin Lamarque

The March 13 race for a U.S. House of Representatives seat is being watched nationally as an indicator of whether Democrats can be competitive in Republican-leaning congressional districts ahead of November elections, when control of both houses of Congress will be at stake.

Trump landed in Pittsburgh and was greeted by Rick Saccone, the state representative and Republican candidate seeking to replace Republican Tim Murphy, who resigned in October amid a sex scandal.

The Republican president spoke briefly with Saccone and his wife on the snowy tarmac before heading off to deliver remarks on tax cuts at an industrial equipment company outside Pittsburgh, where he also gave the candidate a shout-out.

Trump said the company, H&K Equipment in Coraopolis, Pennsylvania, planned a $2.7 million capital investment because of recently enacted corporate tax cuts - one of several examples he gave to show how his first legislative win was helping boost business across the country.

“America doesn’t belong to the Washington power brokers - it belongs to you,” he said in his speech.

Earlier on Thursday, Trump said on Twitter that the trip was meant to show his “total support” for Saccone - although the White House later emphasized that the official purpose of the trip was to talk about tax cuts.

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The distinction is important, because trips that are purely political are paid for by the party, not taxpayers.

“Rick is a great guy. I think he’s going to do really well,” Trump told reporters as he toured the factory before his speech.

Trump said he would be returning to the state to campaign for Saccone, who is facing off against Democrat Conor Lamb, a Marine veteran and former U.S. attorney, in the March election.

Trump won the district by nearly 20 points in the 2016 presidential election and surprised political observers by narrowly winning Pennsylvania, traditionally a Democratic-leaning state.

In an interview with Reuters on Wednesday, Trump pledged to be heavily involved in congressional races, including the one to replace Murphy. Republicans are battling to keep control of both the House and Senate.

Trump’s foray into congressional politics in the U.S. Senate election in Alabama last year did not go well.

After Trump-backed candidate Luther Strange lost to Roy Moore in the Republican primary, Trump switched his support to Moore. The president stood by him even after Moore was accused of sexual misconduct - allegations that the Republican candidate denied.

Moore lost to Democrat Doug Jones in the general election, a stunning result in deeply conservative Alabama and shaving Republicans’ majority in the Senate to 51-49.

On Tuesday, Democrats scored an upset in a Wisconsin state Senate special election in a district Trump won by about 17 points.

Republican Wisconsin Governor Scott Walker on Twitter called the result “a wake up call” for the party there.