White House envoy Steve Witkoff privately warned top Senate Republicans last week that Iran could unleash a mass casualty response if Israel bombs their nuclear facilities, according to a U.S. official and a source with direct knowledge. -snip- Last Thursday, Witkoff held a closed-door briefing on Iran with a group of Republican senators. Among them were Sens. Risch (R-Idaho), Graham (R-S.C.), Barasso (R-Wyo.), and Ricketts (R-Nebr.), the source with knowledge said. Witkoff told the Senators that military strikes by Israel are on the table if no agreement is reached. He then brought up Iran's ballistic missile capabilities. The U.S. is...