Washington (CNN) President Donald Trump is weighing in on the Montana special election this week with a robocall in support of Republican candidate Greg Gianforte.

"Hi, this is President Donald Trump and I know what the people of Montana really want and really care about," Trump said in the robocall. "If you don't vote tomorrow, the liberal Democrats running for Congress will decimate and dismantle all that we've done. ... So get to the polls and vote for Greg. That's Greg Gianforte, you'll be very proud of him for years to come. Thanks a lot!"

The Republican National Committee paid for the ad and is using live callers to comply with state law

Gianforte is challenging Democrat Rob Quist in the special election Thursday to replace Ryan Zinke, the former Montana Republican now running the Interior Department for Trump's administration.

Trump won the Big Sky State last fall by 20 percentage points, and Democrats haven't managed to snag the state's lone House seat in almost 20 years. However, the state's governor is a Democrat who won re-election last fall and one of the state's two senators -- Jon Tester -- is a Democrat, serving his second term. Tester faces re-election next year.

Democrats are seeing a revitalized base after Democrat Jon Ossoff nearly scored a win in a heavily conservative House district in Georgia last month and a better-than-expected performance in a special House election in Kansas earlier in April.

Gianforte, a businessman who made millions when he sold his tech company to Oracle, recently welcomed Donald Trump Jr. at his campaign event.

"The Trump train is chugging along in Montana," Gianforte said. "I look forward to being a voice for Montana and working with Donald Trump to affect those changes."

Vice President Mike Pence also recently campaigned for Gianforte over a two-day swing.