EXCLUSIVE — The outgoing leaders of the Senate’s NATO Observer Group are recommending that Sens. Mike Rounds (R-SD) and Angus King (I-ME) take their place next year, a proposed hand-off that comes at a fraught time in the trans-Atlantic alliance.

Sens. Thom Tillis (R-NC) and Jeanne Shaheen (D-NH), who rebooted the Senate caucus in 2018 and serve as co-chairs, are both retiring at the end of the year, leaving open the question of who will champion NATO in Congress at a time when President Donald Trump has renewed his threats to withdraw from the defensive pact.