In this era of lying who ever knows who is telling the truth?

Michael Cohen, erstwhile personal lawyer for Trump, is the latest prominent figure in Washington to admit he had lied to Congress about Trump's business dealings but is now telling the truth to Robert Mueller, special counsel investigating allegations of collusion between the president's campaign team and Moscow. Reacting to the latest development, Trump says Cohen is lying about lying which presumably means that in Trump's view, Cohen was telling the truth when he appeared before Congress about his business dealings - notably the plan to build a Trump Tower in Moscow when he dismissed any idea that Trump was still talking to the Russians about the monster tower block plan when he was campaigning to enter the White House. Which obviously he shouldn't have been doing. Now Cohen is saying that actually Trump WAS still cosying up to the Russian authorities to build a tower in between campaigning to become president. Cohen says he was lying then but telling the truth now. Trump says Cohen is lying now and telling the truth then!! This is true Alice in Wonderland fantasy stuff. It's impossible to know whether Cohen has ever told the truth about Trump but the fact is he is in trouble with the law and as a result is telling that nice Mr Mueller all kinds of things which I'm sure the former FBI director is lapping up and putting into his huge book of scandals which at some point between now and 2020 he will publish as a best seller and then we can all make up our minds whether it's full of lies or truths, fact or fiction. Trump has already written the speech he will make when the Mueller report is completed. Something on the lines of, "This is all made up, a conspiracy by the Democrat-loving special counsel and his Democrat-loving team of lawyers. The witch hunt is over and I was right all along. The truth is there was no collusion. " But when people say "the truth is" these days, we can't ever again be sure that there is a truth. Cohen said he was speaking the truth to Congress. Now he says he was lying. Why should we believe anything he says?