Beto O'Rourke, the former Democratic Texas congressman who is considering a 2020 White House bid, will join a march to protest US President Donald Trump's rally at the same time in the border town of El Paso.
O'Rourke, who became a Democratic star in 2018 during his unexpectedly close but unsuccessful bid for a US Texas Senate seat, will make a speech lambasting Trump's plans for a border wall as Trump promotes his long-promised barrier at an event nearby on Monday night.
Trump will hold his first campaign rally since November's midterm elections in El Paso as he tried to focus back on a border wall with Mexico.
The duelling rallies come after Trump claimed in his State of the Union speech last week that a border fence separating El Paso from Mexico reduced the city's high crime rate.
The remarks angered local politicians, including O'Rourke and the city's Republican mayor, because El Paso's crime rate was far below the national US average before its border fence was expanded in 2005.
O'Rourke has denounced Trump on Twitter for stoking 'false fear' about immigrants and said the city must use the president's visit to 'tell the true story about the border'.
'We will meet lies and hate with the truth and a vision for the future,' he said in a video over the weekend touting the counter rally.
O'Rourke is due to take part in the March for Truth: Stop the Wall, Stop the Lies event that will pass close to Trump's venue at the El Paso County Coliseum.
The former congressman is scheduled to deliver his speech at around the same time Trump takes the stage.
O'Rourke told Oprah Winfrey in an interview last week that he will make a final decision about running for president by the end of the month.
He would bring fundraising and grassroots firepower to an already crowded Democratic field hoping to take on Trump in next year's election.
Five US senators are among those who have declared their candidacies and other high-profile Democrats, including former Vice President Joe Biden, are mulling bids.
Monday's rallies will follow congressional negotiations due to resume in Washington over a border security funding plan. Talks broke down during the weekend and a Friday deadline looms for lawmakers to avoid another partial government shutdown.