A conservative group is dropping millions of dollars hitting Sen. Jon Tester over his immigration record, just days before the Montana Democrat may have to weigh in on the impeachment of Homeland Security Secretary Alejandro Mayorkas.

One Nation, a group aligned with Senate GOP leadership, is beginning a $15.2 million ad buy on Friday which will run through the summer. The first ad, running statewide on TV and digital, goes after Tester’s past statements and votes on immigration, criticizing his positions on “amnesty,” the border wall and sanctuary cities.

The issue advocacy ad says “tell Sen. Tester, stop supporting Biden’s border disaster,” citing Tester’s past votes on immigration, including the bipartisan Gang of Eight immigration bill. In a statement, One Nation President Steve Law said Tester’s votes “led to the crisis at our Southern border.”

“Senator Tester has repeatedly voted to fund sanctuary cities and grant amnesty to illegal immigrants. He even voted to allow President Biden to stop building the border wall. Senator Jon Tester needs to stop supporting President Biden’s border disaster,” Law said.

One Nation’s big reservation is a spring and summer bridge for Republicans to $48 million in reservations from GOP groups beginning in September. The GOP has largely coalesced around veteran Tim Sheehy after Rep. Matt Rosendale exited the primary.

Senate Majority PAC, a key Democratic group, reserved $27 million in ads in the state as well — signs that the race is likely to go well over $100 million.

Tester is a prodigious fundraiser, and his seat is perhaps Republicans best pickup opportunity in the tight battle for Senate control. With the retirement of Sen. Joe Manchin (D-W.Va.), Democrats essentially need to hold the rest of their incumbent seats to keep the majority.

One Nation’s massive ad buy focuses on a crucial issue, both for Tester and the GOP. The House is expected to send over its impeachment articles for Mayorkas next week, and Tester has said he will support dismissing a trial because he believes Congress has other more important priorities, like the bipartisan border security deal rejected by the GOP.

In fact, Tester has said in recent interviews he’d like to see a revote on that bill, which married border security and foreign aid and was negotiated by Republicans before former President Donald Trump lobbied the GOP to reject the deal.

The One Nation ad urges Tester to instead support the Secure the Border Act, Sen. Ted Cruz’s (R-Texas) Senate companion bill to the House-passed HR 2 legislation, which would restart border wall construction and reinstate the Trump administration’s Remain in Mexico policy. That bill had no Democratic support in the House.

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