A leading Republican super PAC is deploying more ground troops to key districts as threats to the party’s House majority escalate.

Congressional Leadership Fund, affiliated with House Speaker Paul Ryan, R-Wis., is investing an extra $3 million in 15 vulnerable, Republican-held seats as the midterm elections approach, the group told the Washington Examiner on Monday. The funds are underwriting platoons of paid field staff, with the goal of doubling the voters CLF reaches every week as part of a multi-million dollar voter turnout operation in 40 targeted House districts.