The House votes
Opponents need a simple majority, or 218 votes, to reject the deal. There are 246 Republicans in the House, and it’s safe to assume they will all vote against the deal.
The Senate votes
Opponents there need 60 votes against the deal to break a filibuster and reject the deal.
President Obama reviews their decision
If both chambers of Congress reject the deal, Obama will veto their action.
Back to the House
Opponents would need 290 votes to override Obama’s veto. That means opponents need 44 Democratic votes to reject the deal outright.
Back to the Senate
To kill the deal, the Senate would also have to override Obama’s veto, with 67 votes.