The COP21 Paris agreement requires ratification by at least 55 countries representing 55% of total greenhouse gas. Will the US lead by example and ratify the agreement? Politics and law will ultimately decide. At issue is the definition of the word treaty and the unsettled nature of the limits to US presidential executive action. It is a near-certainty that President Obama will ratify the agreement. But it is equally likely that opponents will mount legal challenges to this action. Settling these conflicts includes a political component which complicates matters. The November presidential and congressional elections are key to the timing of resolution of this matter. They are also key to understanding the level of financial commitment the US will provide to global emission reduction. We calculate the likelihood of permanent ratification of the treaty to be about 45% although there is a much smaller likelihood that Congress will fully fund the announced financial pledge.