Almost a month after he found his next starting quarterback, John Elway opened the Broncos’ checkbook to give them help on the other side.



On Monday, the first day of the NFL’s legal tampering period, the Broncos reached a three-year, $33 million agreement with former Houston Texans defensive back Kareem Jackson, according to a source.



The deal, along with the trade for quarterback Joe Flacco, won’t become official until Wednesday afternoon, when free agency begins.



A former first-round pick, Jackson helps to plug a gaping hole in the Broncos’ defensive backfield while giving new head coach Vic Fangio options. Jackson has played safety and corner, and the Broncos have needs at both, thanks to impending departures of corners Bradley Roby and Tramaine Brock, and the recent release of safety Darian Stewart.



The need, however, is greater at corner, where the Broncos have only Chris Harris Jr. and second-year player Isaac...