Theories I have heard for why Nikki Haley abruptly resigned as UN Ambassador

Because of a looming ethics scandal.

Because she no longer fit into Trump’s foreign policy team now that he has Bolton and Pompeo.

Because Trump’s trashing of Christine Blaskey Ford was her last straw.

Because having the entire world laugh at Trump at the UN was her last straw.

Because she is getting buried by personal debt and needs to get to the private sector to make money.

So she can take Lindsay Graham’s Senate seat after Trump fires Jeff Sessions and appoints Graham as AG.

So she can challenge Trump in the Republican primary.

So she can replace Pence as Trump’s vice president.

Because someone in the administration figured out that she was the author of the recent anonymous NYT op-ed.