It is possible, of course, that all these sources are wrong. It is also possible that Cohen did visit Prague, and either did not meet with Russia, or met to discuss innocuous topics, and then lied about it. But the more probable explanation by far is that Cohen did visit Prague and did meet with Russian agents.
What would all this mean? Well, it would mean just about the worst possible thing for Trump. There’s no chance Cohen took such a meeting without Trump’s direction. As Cohen told George Stephanopoulos earlier this month, “nothing at the Trump organization was ever done unless it was run through Mr. Trump” — certainly an international trip to covertly meet Russian intelligence officials would qualify as a matter Trump had to approve. As the previous McClatchy report indicates, Mueller has the evidence of Cohen’s visit to Prague. (Cohen continues to deny ever having visited Prague.)