WASHINGTON — Conservative House Republicans have embarked on an eleventh-hour political maneuver to derail the Iranian nuclear deal, saying they can’t vote on it until the president coughs up copies of side deals Tehran negotiated with atomic inspectors.

The last-ditch effort to snarl implementation of the deal was part of a political spectacle that unfolded on Wednesday in Washington over one of President Barack Obama’s key foreign policy initiatives.

Inside the Capitol, congressional Republicans turned on each other angrily as they moved closer to a vote on the deal, which gives Iran billions of dollars in sanctions relief in exchange for restraints to keep it from becoming a nuclear-armed state.

Outside on the lawn, GOP presidential candidates Sen. Ted Cruz, R-Texas, and Donald Trump whipped up several thousand demonstrators with remarks harshly criticizing the deal. “Never ever, ever in my life have I seen a deal so incompetently negotiated as our deal with Iran,” Trump bellowed on the hot, humid afternoon.

The maneuvering and speechifying did little to change the reality: Barring unlikely success of the House Republicans’ strategy, the international accord will move ahead. Even if Congress succeeds in passing legislation aimed at undermining the deal, Obama would veto it and Democrats command enough votes to sustain the veto.