Donald Trump still thinks his policies can boost American GDP growth to 4 percent, more than double the average rate the U.S. has seen in this century.

In a speech to an energy conference in Pittsburgh on Thursday, the Republican presidential candidate claimed his tax cut and deregulation plans could boost U.S. growth to 4 percent or more. He first made the bold prediction in a speech earlier this month, saying "my great economists don't want me to say this, but I think we can do better" than 4 percent.

Trump, the billionaire developer, has touted himself as a pro-growth candidate and better economic alternative to Democrat Hillary Clinton. Trump has promised broad tax cuts, deregulation of the U.S. energy industry and increased spending on infrastructure and the military, leading he would expand the deficit much more than Clinton would.

Despite those deficit projections, voters have generally felt Trump is better prepared to handle the U.S. economy than Clinton. He held a 46 percent to 41 percent advantage on the issue in the NBC/Wall Street Journal poll released Wednesday.