http://www.bbcnewsd73hkzno2ini43t4gblxvycyac5aw4gnv7t2rccijh7745uqd.onion/news/world-us-canada-64194129
They're introduced by a legislator, assigned to a committee for review and revision, brought to the floor of Congress and further amended, then given an up-or-down vote. That is not how things work very often these days, as massive spending bills are negotiated behind closed doors and passed on short notice and with little debate.