Dow Jones: Oil companies and coal-fired power plant operators would be the likely losers if Democrats expand their majorities in the U.S. Congress and Sen. Barack Obama wins the White House. Obama, D-Ill., has called for a windfall tax on oil company profits and for cutting the greenhouse-gas emissions produced by coal-fired plants. Democrats tried to push similar measures earlier this year, but failed amid opposition from the White House and Senate Republicans, who commanded a substantial …