GREAT FALLS, (AP) — President Donald Trump declared it was “time to retire” U.S. Sen Jon Tester on Thursday as he campaigned in Montana against the lawmaker he blames for derailing his nominee to lead the Department of Veterans Affairs.

Appearing in a state he won by roughly 20 points in 2016, Trump cast Tester as a “liberal Democrat,” railing against his voting record on issues like abortion, immigration and taxes. While Tester voted against Trump’s Supreme Court nominee Neil Gorsuch and the Republican tax bill, he is considered a more centrist member of the caucus.

Tester tried to counter that narrative before Trump got to the state by taking out a full-page ad in more than a dozen newspapers across the state thanking him for signing 16 bills the Democrat sponsored or co-sponsored.

Trump rallied in Great Falls on Thursday to boost the candidacy of Tester’s Republican challenger, state Auditor Matt Rosendale. The president has made the Montana race a priority as he hopes to help Republicans tighten the party’s hold on the Senate.

“You deserve a senator who doesn’t just talk like he’s from Montana. You deserve a senator who votes like he’s from Montana,” Trump said.

Trump’s eldest son, Donald Trump Jr., received deafening applause as he opened his father’s rally, quickly going on the attack against Tester and welcoming Montana Republicans Sen. Steve Daines and Rep. Greg Gianforte onto the stage.

Tester’s ad sought to undermine Trump’s efforts to boost Rosendale by pointing out that he and the president agree on several issues. Trump blames Tester for derailing his nomination of White House physician Ronny Jackson to lead the VA.

“Welcome to Montana, and thank you President Trump for supporting Jon’s legislation to help veterans and first responders, hold the VA accountable, and get rid of waste, fraud and abuse in the federal government,” the ad read.

The Tester campaign also planned a statewide radio ad campaign to run through the weekend touting his bills that Trump has signed.

Hundreds of people began lining up outside the arena a full eight hours before Trump was scheduled to speak. The number swelled to thousands by midday. Mechanic Shane Hegle said he drove 120 miles (195 kilometers) from his Cut Bank Home to be among the first in line.

Hegle said he voted for Tester in past elections but was undecided this time. Trump’s message will influence his decision, he said.

“This is going to help a bunch,” Hegle said. “I’ll see what Trump has to say and how he delivers his magic words.”

Before the arena gates opened, about three dozen protesters stood behind police tape about a quarter of a mile away and tried chanting to compensate for being out of sight from those waiting in the long line.

Tester is one of 10 Senate Democrats running for re-election in states that Trump won in the 2016 election. Trump singled out Tester in April, saying the farmer from Big Sandy “will have a big price to pay” for releasing allegations against Jackson that included drunkenness, overprescribing medication and fostering a hostile work environment. Jackson, a Navy rear admiral, denied the claims but withdrew his nomination. The Pentagon is investigating.

Montana is the latest stop on Trump’s midterm campaign tour, designed to boost Republicans and advocate for his first 18 months in office. He recently made a similar trip to North Dakota and is expected to travel throughout the summer.

Rosendale, who is seeking to deny Tester a third term and give Montana an all-Republican congressional delegation, said Trump has focused on the race because of Tester’s “liberal obstruction.”

Montana, which elects both Republicans and Democrats to statewide office, strongly supported Trump in the 2016 presidential election, leading both Senate candidates to compete for Trump supporters. Rosendale said he’ll back Trump’s agenda, while Tester said he’ll support the president when it’s in the state’s interests and oppose him when it’s not.

Tester planned to spend Thursday listening to farmers’ and business owners’ concerns about Trump’s import tariffs and was expected to be driving back to his farm at the time of Trump’s rally, spokeswoman Marnee Banks said.

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Associated Press writer Darlene Superville in Washington contributed to this report.