By Pete Schroeder and Michelle Price WASHINGTON (Reuters) – An aggressive regulator is critical to maintaining the United States as the “gold standard” for capital markets, U.S. Securities and Exchange Commission (SEC) chair Gary Gensler will tell the U.S. Senate Banking Committee on Thursday. Gensler will appear before the panel for its regular oversight duties, but the hearing comes at a time of Republican frustration over his agenda. They claim he has overstepped his authority with a broad assault on U.S. capital markets and adopted a hostile stance toward the financial industry. Republican…