SPRINGFIELD — A historical marker dedicated Wednesday on the grounds of Illinois’ Old State Capitol commemorates the date when then-U.S. Sen. Barack Obama announced his 2008 presidential bid there.The marker in downtown Springfield notes the future president’s Feb. 10, 2007, announcement and Obama’s Aug. 23, 2008, introduction there of his running mate, Joe Biden.Illinois House Speaker Emanuel “Chris” Welch, the first Black legislator to hold that position, said during the ceremony that …