By Richard Cowan and David Morgan WASHINGTON (Reuters) – The day before former President Donald Trump’s impeachment trial begins on a charge of inciting the deadly attack on the Capitol last month, his lawyers on Monday denied he had encouraged violence and challenged the constitutionality of the trial now that he has left office. Trump’s lawyers accused the nine Democratic lawmakers known as “impeachment managers” who will prosecute him of “intellectual dishonesty and factual vacuity” in their portrayal of Trump’s fiery Jan. 6 speech to a crowd of his supporters before hundreds stormed the Ca…