How did Sen. John McCain, the onetime front-runner for the Republican presidential nomination, come to this? New polls this week showed support for him plummeting in two key early-voting states. Tied for fifth place in Iowa, with 6 percent. Falling to fourth place in South Carolina, with 7 percent. Mason-Dixon Polling & Research conducted both polls of likely Republican voters, which had error margins of plus or minus 5 percentage points. This after an ongoing Senate debate on immigration that highlights McCain's opposition to his party's base on a hot-button issue, and the informal entry into the race of former...