LOS ANGELES (MarketWatch) - Republican presidential candidate Sen. John McCain on Thursday called for the firing of Securities and Exchange Commission Chairman Christopher Cox, saying he has "betrayed the public's trust."

McCain castigated the SEC for letting speculators "turn our markets into a casino," allowing naked short selling and eliminating the uptick rule to protect investors.

In an attempt to beef up his economic credentials after taking a few hits earlier this week for saying the nation's "fundamentals are strong" while the stock markets were suffering huge losses, McCain got more aggressive, saying that the SEC was "asleep at the switch" and reiterated his call for tougher oversight of Wall Street. McCain made the statement, while campaigning in Cedar Rapids, Iowa, as he is losing ground in polls to his Democratic opponent, Sen. Barack Obama.

McCain castigated the SEC for letting speculators "turn our markets into a casino," allowing naked short selling and eliminating the uptick rule to protect investors.