 FORMER PRESIDENT TRUMP SPOKE WITH UKRAINIAN PRESIDENT ZELENSKY. CBS'S ROBERT COSTA TELLS US ZELENSKY CONGRATULATED HIM ON BECOMING THE GOP NOMINEE AND CONDEMNED SATURDAY'S ATTEMPTED ASSASSINATION. THIS IS POTENTIALLY A SIGNIFICANT EXCHANGE. TRUMP HAS LONG BEEN WORRY OF U.S. INVOLVEMENT IN UKRAINE AND PRESIDENT BIDEN HAS MADE IT A KEYSTONE OF HIS RECORD. IF TRUMP STARTS TO BUILD A REPORT WITH ZELENSKY, IT COULD QUIET SOME CONCERNS. CBS NEWSBREATH. I'M STACY LYNN.