What We're Following This Morning

Iowa caucuses: Voters in the state head to caucus this evening, the culmination of months of campaigning by presidential candidates from both parties. Polls show Trump leading the Republican field and Clinton the Democratic. For an explanation of how the caucuses work, go here.

A meeting on Zika: The World Health Organization will hold an emergency meeting today to discuss whether the virus is a public health emergency of international concern. That classification would require a global response to the virus that is spread to people through mosquito bites. The virus has also been linked to birth defects in Brazil. Update: More here

What caused last year’s Amtrak derailment?: The NTSB will release documents on the May 12, 2015, derailment that could shed light on what caused the crash. The train was traveling at about twice the posted speed when the derailment occurred in Philadelphia, killing eight people and injuring about 200 others.