By Jarrett Renshaw

Oct 10 (Reuters) - U.S. President Donald Trump on Thursday will hold his first campaign rally since Democrats launched an impeachment inquiry against him, choosing a large arena in a Democratic stronghold in Minnesota to mount his latest public defense.

Supporters of the Republican president will gather inside the 20,000-seat Target Center in Minneapolis for the 7 p.m. CDT rally, while protesters promise to voice their opposition outside.

Trump's path to re-election in November 2020 depends on clinching a cluster of farm and Rust Belt states decided by slim margins in 2016. Minnesota, which Trump lost by 1.5 percentage points to Democrat Hillary Clinton, is a key target, his campaign said.

Unlike 2016, when it spent little money and time in the Midwestern state, the campaign has already hired staff and organized voters there. Thursday's visit marks the president's fourth trip to the state in the past 16 months.

The visit comes against the backdrop of an impeachment investigation by the Democratic-led U.S. House of Representatives that has upended Washington.

The probe centers on a whistleblower's allegations that Trump used military aid to secure a promise from Ukraine's president to investigate former Vice President Joe Biden, a leading candidate for the 2020 Democratic presidential nomination, and his son Hunter, who was on the board of a Ukrainian energy firm.

Trump has denied wrongdoing. The White House said on Tuesday it would refuse to participate in the "partisan and unconstitutional" impeachment inquiry.

Alex Conant, a Republican strategist born in Minnesota, said the rally venue held a symbolic meaning.

"I think he wants to have the biggest crowd possible. If he gets 15,000 to 20,000 people on a Thursday night in Minneapolis, that sends a signal," Conant said.

Trump's visit has generated local backlash. The city's mayor was criticized for initially suggesting Trump was not welcome. The Minneapolis police union began selling pro-Trump T-shirts after the police chief said off-duty officers could not wear their uniforms to political events.

Vice President Mike Pence, who is also making a visit to Minnesota on Thursday, is scheduled to meet with the police union.

City and state leaders are holding several news conferences on Thursday to highlight Democratic causes and publicly reject Trump's platform. Local labor leaders are planning a late-afternoon march to protest Trump's visit.

"I believe in the people of Minnesota. In the end, I think we will see people voicing their opinions without any incident," said Amy Koch, a Republican strategist in Minnesota who plans on attending the rally.

No Republican presidential candidate has won Minnesota since Richard Nixon in 1972.

A poll released by Alliance for a Better Minnesota on Wednesday showed 52% of registered voters in the state would vote for the Democratic candidate next year, while 42% would vote for Trump. The survey of 1,175 voters was conducted with the left-leaning Public Policy Polling.

(Reporting by Jarrett Renshaw in Philadelphia; Editing by Colleen Jenkins and Peter Cooney)

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