Thirteen major military and veterans groups have joined forces to try to force one senator — Republican Tom Coburn of Oklahoma — to release a hold that he has placed on a major veterans benefits bill.Coburn has been identified by Senate aides as the lawmaker preventing consideration of S 1963, the Veterans’ Caregiver and Omnibus Health Benefits Act of 2009, by using an informal but legal practice of putting a hold on a bill.Coburn’s staff did not respond to questions, but Senate aides said the first-term senator has expressed concern about creating new and unfunded benefits and wants the opportunity to amend the measure.One of Coburn’s suggestions is to divert money from unspent economic and job stimulus programs to cover costs of new benefits for veterans and their families, according to sources who have discussed the issue with Coburn’s staff.