By Luc Cohen and Sarah N. Lynch (Reuters) -Donald Trump’s bid to impede a criminal investigation into his possession of documents taken from the White House has begun to unravel, legal experts said, after courtroom setbacks including doubts expressed by judges about the former U.S. president’s claim that he declassified records seized at his Florida home. Trump has experienced disappointments on multiple fronts this week as his lawyers try to slow down the Justice Department investigation that kicked into high gear with an Aug. 8 court-approved search of his Mar-a-Lago residence in which FBI a…