Democratic proponents of Obamacare deny that a vote by House Republicans to fund the government while defunding Obamacare will have any policy significance, but the Senate conservatives who have long called for such a vote believe they have the opportunity to attack Obamacare in a way that delivers a policy victory for opponents of the law.

Senate Majority Leader Harry Reid, D-Nev., and his caucus will doubtless defeat the proposal, an outcome that Republicans desire because it will force vulnerable Democrats to take an unpopular vote.