Actually Trump should try to use the Hillary Clinton excuse. It would prove him extremely guilty. Since unlike Hillary's emails, they had no classified stamps (headers and footers) on the documents, where Trumps documents are clearly stamped Classified, Secret, Top Secret and even TS/SCI on them.
Of course Trump could claim he declassified everything in his possession, but never allowed his staff to actually change their classification.
It's just like when Trump ordered Don McGahn to fire Robert Mueller. But McGahn never fired Mueller. The Mueller firing, even though Trump had ordered it, was never carried out. The same goes for declassifying information. If those he ordered to declassify the documents, fail to do so.