washington co-founder firm commission dossier donald trump presidential campaign last year vacation testify senate judiciary committee hear russia probe next week lawyers say letter release friday glenn simpson fusion gps vacation july 31 travel abroad aug. attorneys say letter add profoundly disturb hear expand due partisan agendas include allegations russian meddle u.s. election possible tie trump campaign russia donald trump jr. president donald trump one-time campaign manager paul manafort due testify day simpson attorneys ask simpson excuse appear add allegations fail register foreign agent nothing effort smear him man whose firm behind trump dossier wo n't testify senate lawyer