Explainer-What are NATO's next steps if Russia invades Ukraine?

FILE PHOTO: Airmen from the 4th Fighter Wing at Seymour Johnson Air Force Base, N.C. and the 48th Fighter Wing, Royal Air Force Lakenheath, England, arrive at Amari Air Base, Estonia, January 24, 2022. U.S. Air Force Photo/Staff Sgt. Megan Beatty/Handout via REUTERS

BRUSSELS (Reuters) - NATO allies are putting forces on standby https://www.reuters.com/world/europe/nato-sends-ships-jets-eastern-europe-ukraine-crisis-2022-01-24 and sending reinforcements to eastern Europe in response to Russia's buildup of more than 100,000 troops on Ukraine's borders.

Here are some of the dilemmas about NATO's next steps.