They had been set to go in September but decided to go today to shore up support for the war under the new assault from the Democrats and the chief defeatist, Reid. They plan to meet with members of the Senate and urge them to continue supporting the war:

Veterans of the Iraq War from across the United States will be on Capitol Hill on Tuesday, July 17, to urge Senators to support the mission in Iraq and to wait until General Petraeus reports to Congress in September on the progress of the “surge” before taking a defeatist position.
“I know senators on Capitol Hill are feeling the heat to retreat from Iraq,” says Pete Hegseth, an Iraq war veteran and Executive Director of Vets for Freedom. “But if they think it’s hot in Washington, DC, try fighting Al Qaeda and company in Iraq. Our soldiers-and their new strategy-need support from Congress, not political pandering. The fact is the surge is showing early signs of success and our troops in the field need the support of our nation’s lawmakers as they fight our nations enemies in Iraq.”
Vets for Freedom is a nonpartisan organization established by combat veterans of the wars in Iraq and Afghanistan.

Those of you who believe that the troops think the war is a lost cause might want to note that the Vets for Freedom has about 10,000 members (that’s a link to the first hour of the Hugh Hewitt show, he interviewed Pete Hegseth of Vets for Freedom yesterday).