WASHINGTON (Reuters) - After a disastrous loss for Republicans in Alabama last month, President Donald Trump will again wade into congressional politics on Thursday when he travels to western Pennsylvania to signal support for the Republican candidate in a special election there.

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While Trump will tour an industrial equipment company outside of Pittsburgh to tout the tax-reform legislation passed by Congress last month, the visit comes amid a contest to replace Representative Tim Murphy, who resigned in October amid a sex scandal.

The president will be met on arrival by Rick Saccone, a state representative and the Republican candidate to replace Murphy in the U.S. House of Representatives. The Democratic candidate in the March 13 election is Conor Lamb, a Marine veteran and former U.S. attorney.

The race is being watched nationally as an indicator of whether Democrats can be competitive in Republican-leaning congressional districts ahead of November’s midterm elections, when control of both houses of Congress will be at stake.

Trump won the district by nearly 20 points in the November 2016 presidential election and surprised political observers by winning Pennsylvania, traditionally a Democratic-leaning state, by less than 1 percent.

In an interview with Reuters on Wednesday, Trump pledged to be heavily involved in the year’s congressional races, including the one to replace Murphy.

“I am going to spend probably four or five days a week helping people because we need more Republicans,” he said.

Trump’s last foray into congressional politics did not go well.

In a special U.S. Senate election in Alabama late last year, the president first backed the incumbent candidate in the Republican primary, Luther Strange, who had been named temporarily to fill the seat vacated by Jeff Sessions when Trump named him U.S. attorney general.

After Strange lost to Roy Moore, 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 shocking result in deeply conservative Alabama and shaving Republicans’ majority in the Senate to 51-49. Exit polls showed that many voters turned out to register their disapproval of Trump.

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 was “a wake up call” for the party there.