The stock market got off to a rocky start on Wednesday. Major indexes fell across the board, with the Nasdaq Composite (NASDAQINDEX: ^IXIC) leading the way lower with a drop of nearly 2.5% at midday. Other stock market benchmarks posted somewhat more modest declines.

The move came in the aftermath of news from late Tuesday that the credit rating of the sovereign debt issued by the U.S. Treasury had been downgraded. After initially downplaying the decision from credit rating agency Fitch Ratings, stock markets later moved lower, while bond market yields climbed.

Here's a closer look at what happened and whether you and other investors should be concerned about the downgrade.

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Source Fool.com