For President Donald Trump, this week stands to be not only one of the most consequential of his presidency on the international stage, but also perhaps in domestic policy as well. Much political attention has been focused in recent days on Trump's decision to strike nuclear sites in Iran.

The Byrd Rule, adopted in 1985, is a procedural constraint named after the late Senator Robert C. Byrd of West Virginia to prohibit “extraneous” provisions from being tacked onto reconciliation bills, which are fast-tracked budget packages that allow legislation to pass with a simple majority, bypassing the 60-vote filibuster threshold.