The invitation should have been declined on the grounds, that PM Netanyahu is sensitive to the proximity of the planned date, to that of the upcoming Israeli elections, and therefore would be inappropriate in light of that. At the same time PM Netanyahu should definitely go ahead and address the annual meeting of AIPAC, which every Israeli PM addresses every year, and try and find some other timing to address a joint session of the Congress.
It still can be done, with careful wording and some finesses, though no doubt, that at this later time, it will unfortunately (and somewhat correctly) be interpreted as bowing down to local political and American administration pressure. Having said that, it is probably still the stately thing to do.
By Noam A. Rotem
(I was thinking this to myself already on Thursday, before the torrent of criticism that started pouring in over the Israeli weekend. Now if he backs down, at this later hour, he looses, the nobility that could have been achieved with an earlier declination)