I think Jonathan Turley answers that question best; great article to read in it's entirety:
When William Shakespeare wrote that “all the world is a stage” and “one man in his time plays many parts,” he could have probably had in mind Senator Charles Schumer. In 1999, the Democrat from New York famously opposed witnesses in the trial of President Clinton as nothing more than “political theater.” Now Schumer has declared that witnesses and a full trial are essential for President Trump, and that a trial without witnesses would be deemed the “most unfair impeachment trial in modern history.”
That does not include the Clinton case where Schumer sought to proceed to a summary vote without a trial. As the Senate now gears up for the third presidential impeachment in history, the fight has begun over the rules and scope of a trial. The Framers were silent on the expected procedures and evidence for a trial, beyond the requirement of a two-thirds vote to convict a president. The only direct precedent on these issues is derived from two very different trials, those of President Johnson and Clinton.
By sending a thin record to the Senate, the House could not have made things easier for Trump. Since the House did not take time to subpoena critical witnesses, such as former national security adviser John Bolton, or to compel testimony of other witnesses, the Senate could simply declare that it will try the case on the record supplied by the House, a record that Democrats insist is already conclusive and overwhelming. Moreover, in reviewing the past trials of Johnson and Clinton, Democrats may have to struggle with precedents of their own making. Indeed, Republicans could argue that a trial without witnesses is impeachment in Democratic style.
https://thehill.com/opinion/judicia...-the-real-challenge-to-full-impeachment-trial
