In a new nationwide Zogby International poll released today, Barack Obama has taken a double-digit lead over John McCain:

Democrat Barack Obama has sprinted out to a 10-point lead over Republican John McCain in a four-way presidential contest including Libertarian Bob Barr and Liberal Ralph Nader, the latest Reuters/Zogby telephone poll of likely voters nationwide shows.

Obama does well among his Democratic base, winning 79 percent support — an indication that the party faithful may be coming together behind his campaign as a bruising nomination campaign nears the end. He also does well among nonaligned voters, as independents favor him over McCain by a 48 percent to 32 percent margin.

Obama leads in the East, the West and in the South, while the two are essentially tied in the central part of the country, including the Midwest and the Great Lakes region, the poll shows. He leads among all voters under age 65 — including by huge percentages among those voters under age 30 — but trails McCain among those older voters by a 45 percent to 34 percent margin. Interestingly, Obama holds a 13-point edge among those voters age 50 to 64.

The survey hints that Libertarian Bob Barr could do some serious damage to McCain by stealing support among the very conservative and libertarian voters. Barr wins 10 percent support among those self-described “very conservative” voters, and wins 22 percent among philosophical (not necessarily “capital L”) libertarians.