She served as Assistant Secretary of State for Western Hemisphere Affairs from October 15, 2018[1] until her resignation in August 2019.

Breier replaced Francisco Palmieri, who was acting interim since the beginning of Trump's presidency in January 2017.

[4] On January 30, 2019, Breier tweeted support for Canada, following their decision to reduce its embassy staff in Havana, Cuba, after a 14th Canadian diplomat reported symptoms of the mysterious Havana syndrome in late December 2018.

[6] News reports cited her resignation due to internal disputes over immigration policies.

[7][3] She also fought with National Security Council official Mauricio Claver-Carone over the administration's Venezuela policy.