Worst one-day point drop since Dec. 2008

WILLIAMS: Good evening.

BRIAN WILLIAMS, anchor: This was a dark day for the nation's finances and for millions of Americans with a financial stake in the markets, the very same Americans who are still processing the fact that our country has lost its top credit rating . Here's

the damage from today: The Dow down over 634 points, that's the sixth largest point drop in its history, the worst since '08. Nasdaq lost just about 7 percent of its total value. S&P 500 lost 6.6 percent of its value in one day.

WILLIAMS: The president went on television at midday to reassure Americans , but the damage was done. The markets continued to drop while he spoke, and the damage continues. It's a bigger systemic problem with no real end in sight. We begin our coverage tonight with CNBC 's Maria Bartiromo . She's at the New York Stock Exchange . Maria , you won't see many days like this one in your lifetime.

MARIA BARTIROMO reporting: It's true, Brian . What day today on Wall Street . After last week's sell-off and the credit downgrade by Standard Poors late Friday, anxieties had mounted over the weekend and all eyes were on Wall Street this morning. Stocks dropped right at the opening bell on Wall Street as the selling that started Thursday just kept going. Not a single stock on the S&P 500 ended in positive territory.

Unidentified Reporter: That's really bringing the market into the red.

Mr. ART CASHIN (UBS Director of Floor Operations): There's concern that the S&P downgrade may do something to consumer confidence and thereby ease us a little closer to the infamous double dip that everybody's worried about.

President BARACK OBAMA: Good afternoon, everybody.

BARTIROMO: President Obama came out to reassure investors.

Pres. OBAMA: This is the United States of America. No matter what some agency may say, we've always been and always will be a AAA country.

BARTIROMO: And while the markets sold off another 400 points after the president's speech, sales of US Treasuries remain strong, easing fears that interest rates might rise on mortgages, cars and student loans.

Mr. PETER FISHER (Blackrock, Inc.): If the world's a risky place and investors are going to shed risk, they're not going to shed the least risky asset, which is still US Treasury securities .

BARTIROMO: In an attempt to avoid a recession in Europe , the European Central Bank bought bonds to keep Spain and Italy afloat, but that may not be enough.

MICHELLE CARUSO-CABRERA reporting: There's going to be a bigger burden on France and Germany . And the question is do they have enough money, do they have the will to bail out the other countries?

BARTIROMO: Some investors sought safety in gold, sending gold prices up more than $61 to a new record high, while oil closed just above $81 a barrel.

$61.40 $1,710.20 Today

$5.57 $81.31 a barrel

Mr. DAN ARBESS (Perella Weinberg Partners): Look around, the compass is spinning and investors are being turned upside down.

BARTIROMO: Despite the chaos, investor Dan Arbess sees one possible advantage to the downgrade.

Mr. ARBESS: Some day we will thank S&P for the credit downgrade. Is -- it is a message to Washington that we must begin to address the long-term solvency of the United States of America.

BARTIROMO: Next big event to watch, the Federal Reserve will meet tomorrow in its regularly scheduled meeting. Investors will be paying close attention to see if the fed says anything about the economy and whether it requires additional stimulus right now, Brian .

WILLIAMS: All right, Maria Bartiromo starting us off from the floor of the exchange. Maria , thanks.