From NBC's Domenico Montanaro
Whether Romney's 282 delegates can be given to McCain depends on each state's rules on "releasing" delegates, per the RNC.
Language to watch for during Romney's endorsement is if he says he is "releasing" his delegates "to McCain." That, or some variation, may be enough in some states where he won BOUND delegates.
Caucus states' rules are less restrictive and several of these states' delegates are completely unbound and may be able to go to whomever they so choose.
Here are the primary state delegates Romney has won: Ark. (1), Calif. (6), Ga. (3), Ill. (3), Mass. (22), Mich. (23), N.H. (4), Tenn. (8) and Utah (36).
Caucus state delegates won: Alaska (12), Colo. (43), Iowa (7), Maine (18), Minn. (38), Mont. (25), Nev. (17), N.D. (8), Wyo. (8).
Of these, all of the primary delegates are pledged. But, of the caucuses, the following are not bound: Colorado, Iowa, Maine, Minnesota, Nevada and Wyoming.
*** UPDATE *** Highlighting how complicated this all can be, the Massachusetts Republican Party, said once Romney says his delegates can be released, then they are no longer bound to him, BUT they aren't sure if they would be legally bound to McCain -- if Romney so urges -- or if they can vote their conscience. They are checking.
*** UPDATE 2 *** For perspective, NBC News' Election Unit reminds us that in many states, the actual delegates -- the actual people who will sit at the convention and vote -- have not been elected yet. Even in a state where Romney won pledged delegates, unless they are actually elected already, the next phase could elect delegates who are McCain, Huckabee or uncommitted or something else. And in many states, it's not likely that a candidate who releases his delegates could "bind" them to another candidate.