The departure of John Bolton, President Trump's third national security adviser, injects still more volatility into U.S. foreign policy, and the choice of his successor has profound implications for U.S. national security interests.

The big picture: Bolton successfully influenced U.S. withdrawals from the Iran nuclear deal, arms control treaties and international agreements, while chipping away at American commitments to multilateralism. But he had become marginalized in the White House as his hawkish approach increasingly clashed with Trump's deal-making instincts.

Frances Z. Brown
Frances Z. Brown is a senior fellow and co-director of Carnegie’s Democracy, Conflict, and Governance Program, who previously worked at the White House, USAID, and in nongovernmental organizations. She writes on conflict, governance, and U.S. foreign policy
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Context: Bolton ended up on the losing side of a growing list of policy disputes. Reports suggest the final straw came after Bolton protested proposed meetings between Trump and the Taliban and between Trump and Iranian President Hassan Rouhani.

  • Bolton had already been sidelined from Afghanistan policy deliberations as Secretary of State Mike Pompeo advanced a deal with the Taliban (though Trump ultimately called off the Camp David meeting on Saturday).
  • After Iran downed a U.S. surveillance drone this summer, Bolton, long an advocate of military action, argued for a retaliatory strike. Trump approved the strike but then immediately called it off.
  • While Trump has touted his warm relationship with North Korean leader Kim Jong-un as a pathway to productive negotiations, Bolton condemned reports that the U.S. would consider concessions before North Korea abandons its nuclear program.

Between the lines: Perhaps most consequential, reports suggest Trump didn’t have personal chemistry with Bolton — an insurmountable hurdle in this White House. (Bolton and Trump even offered conflicting accounts of Bolton’s departure.)

What to watch: A key question is how Bolton's successor will figure into administration decision-making.

  • Traditionally, the national security adviser has coordinated foreign policy across the government and developed policy options for the president. Bolton, however, rejected these functions in favor of a more public-facing and solitary role — often dispensing with interdepartmental meetings and leaving the parts of the U.S. foreign policy machinery out of sync.
  • Trump could return the position of national security adviser to its more conventional role, restoring a measure of order to the foreign policy process. Alternatively, he could select a candidate who shares his “disruptor-in-chief” instincts or hails from the television commentariat.

This article was originally published in Axios.