A Green Party Senate candidate in Montana was on the state Republican Party’s payroll and now leads an anti-property tax group.

Timothy Adams, the treasurer of Montanans Against Higher Taxes, filed his campaign papers Monday to challenge Democratic Sen. Jon Tester in November, The Associated Press reported Tuesday.

Tester faces an uphill challenge in a state President Donald Trump carried by 21 points in 2016, according to Inside Elections with Nathan L. Gonzales. A Green Party candidate could threaten to tear off a chunk of his voting bloc.

Green Party candidate Jill Stein took 1.6 percent of the votes in Montana in the 2016 presidential election, half a percentage point higher than her national average.

The Green Party officially qualified as a political party in Montana on Monday, the last day candidates could file for office. Party officials sent an e-blast that morning soliciting candidates who could register by the end of the day, the AP reported.

Adams was on the payroll of the Montana Republican State Central Committee from October 2013 through May 2015, though his role within the party is uncertain.

Steve Kelly of Bozeman also filed to run as a Green Party candidate Monday.

“We will absolutely vet both of those candidates,” state party coordinator Danielle Brock told the AP.

Adams briefly ran as a Libertarian candidate in a Montana state House race in 2012 before withdrawing.