Less than a week after the Des Moines Register’s Iowa Poll found the leads of John Edwards and Mitt Romney growing in their respective party presidential bids, the eighth in a series of monthly American Research Group (ARG) polls finds Hillary Clinton with nearly a double digit lead, and Giuliani and Romney in a dead heat.

Clinton received 30 percent of the measured support in the ARG poll of 600 likely Democratic caucus voters, surveyed July 26-30. ARG has measured Clinton’s support at or above 30 percent in seven of its eight polls since December 2006. John Edwards registered at 21 percent—he has only eclipsed the 30 percent mark once in ARG polling (March 2007).

The other big story coming out of this new poll on the Democratic side of the ticket is New Mexico Governor Bill Richardson’s showing at 13 percent—just 2 points below Barack Obama. Richardson’s support had never been measured in double-digits by ARG previously, and more than doubles his June 2007 showing (5 percent).

The Republican side of the ticket is also in flux. Rudy Giuliani (22 percent) and Mitt Romney (21 percent) swap positions compared to June’s ARG survey, with Romney falling 4 points and Giuliani rising 4 points.

John McCain appears to have stopped the bleeding for the moment. After falling in three straight ARG polls—from 29 percent in March to 26 percent in April to 25 percent in May to 13 percent in June—McCain gained 4 points in July, coming in third at 17 percent. Fred Thompson registered in fourth at 13 percent.

Expect a lot more movement among the Democrats and Republicans in the coming months. Overall 15 percent of likely Democratic and Republican caucus voters were undecided as to which candidate they would support—the second highest level of undecided likely voters for each party in ARG’s eight months of polling.