How can I maintain ModelState with RedirectToAction?

[AcceptVerbs(HttpVerbs.Post | HttpVerbs.Delete)]
public ActionResult Delete([ModelBinder(typeof(RdfUriBinder))] RdfUri graphUri)
{
    if (!ModelState.IsValid)
        return Index(); //this needs to be replaced with something that works :)

    return RedirectToAction("Index");
}

...
   if (!ModelState.IsValid)
       TempData["ViewData"] = ViewData;

   RedirectToAction( "Index" );
}

 public ActionResult Index()
 {
     if (TempData["ViewData"] != null)
     {
         ViewData = (ViewDataDictionary)TempData["ViewData"];
     }

     ...
 }

return View("Index");

return Index();