Republican leaders are quietly bunkering down for a fight over Russia sanctions. Defense Secretary James Mattis has asked the House Armed Services Committee Chairman Mac Thornberry to put a provision into the National Defense Authorization Act (NDAA) that would let the administration waive sanctions for U.S. partners, like India and Vietnam, who buy weapons from Russia. And Thornberry has agreed to do so.

Why this matters: In this political environment, anything Russia-related can be explosive. Republicans involved in the conversations tell me they worry that Democrats will use the issue to bash them as appeasing Putin.

• A senior Democratic aide emailed me: "Yes, we are concerned that R [Republican] efforts to chip away at the integrity of Russian sanctions that were passed with the overwhelming majority of support from Congress last summer indeed shows that they are more concerned about appeasing Trump and supporting his efforts to appease Putin."
• Behind the scenes: The aide told me Democrats are still formulating their strategy on the Russia sanctions. Senate Democrats like Bob Menendez and Republican Russia hawks, particularly in the Senate, may oppose the waiver.

What we're hearing: I spoke to Thornberry this morning. He told me he plans to include in his "chairman's mark" of the NDAA on Wednesday "a very limited waiver for the Secretary of Defense, if he believes that a country that is trying to move in our direction still needs to get some sustainment and logistical support for the Russian equipment that they already have."

• Thornberry told me that "part of the problem" with the sanctions bill Congress passed last fall is that "if the Indian military has Russian helicopters and they need to keep them flying they have to do business with the Russian military."
• A source with direct knowledge told me the NDAA will include new sanctions targeting Russia’s arms industry.

Mattis' spokeswoman Dana White told me the Secretary appreciates Thornberry’s support and "wants to avoid any legislation that inadvertently punishes nations with which we are working to expand our defense cooperation." (Meaning India.)

What's next: Unless Mattis and Co. sell Democrats and hawkish Republicans on the waiver, you'll see a brawl.