Wall Street’s main indexes tumbled on Tuesday as investors questioned lofty tech valuations after the CEOs of top Wall Street banks warned of a stock market selloff, while AI favorite Palantir’s sales forecast failed to impress investors.The Dow Jones fell 436.01 points, or 0.92%, to 46,894.82; the S&P 500 dropped 81.71 points, or 1.19%, to 6,767.31; and the Nasdaq declined 398.08 points, or 1.67%, to 23,422.70.