Billionaire Carl Icahn, with four decades of investing under his belt, appeared Tuesday on CNBC's "Fast Money Halftime Report. ": The stock market entered its third day of huge sell-offs and volatility on Tuesday. A day after plummeting 1,600 points, the Dow Jones industrial average opened lower, plunging as much as 567 points and dipping into correction territory before quickly swinging 367 points higher. The index has since been Icahn, an activist investor who often pushes for changing struggling companies, was an early supporter of for president and a confidant during the 2016 campaign.