US President Donald Trump has capped opening night of the unusual Republican midterm convention by making the extraordinary pledge to pay every adult American $5,000 if his party retains its control of both chambers of Congress after November. The billionaire leader coupled his claim with a plea for his supporters to "pretend" he was on the ballot. "If the Republicans win, you win with us and you get $5,000. It will be called the Trump dividend," he told the convention in Dallas, as the party struggles in polls against the Democrats. The proposal, which could cost at least $1 trillion, is seen financially and politically implausible. The president did not specify where the money would come from, citing only that "our country is making so much money."