One of the Republican's major defenses on behalf of Trump , undoubtedly what they put forward as the "best" one, is that he told Gordon Sondland in a Sep. 9th phone call that there was no quid pro quo, and that he wanted "nothing" from Zelensky.
Something else happened on Sep 9th. That was the day the whistleblower complaint was revealed to the House Intelligence committee.
Sept. 9 — Atkinson, the inspector general of the intelligence community, notifies the House intelligence committee that he received a whistleblower’s complaint relating to an “urgent concern” on Aug. 12. He says he found the information credible, and sent “my determination of a credible urgent concern” along with a copy of the complaint to Acting Director of National Intelligence Joseph Maguire, who had seven days to forward the complaint to Congress. But, contrary to “past practice,” Maguire did not forward the complaint to Congress, believing “the allegations do not meet the definition of an ‘urgent concern’ under the [whistleblower] statute,” Atkinson writes. The inspector general says he will keep the committee apprised of his attempts to resolve the issue. https://www.factcheck.org/2019/09/the-whistleblower-complaint-timeline/
When Sondland spoke to Trump on Sep. 9th, and Trump told him "no quid pro quo", Trump knew that the 'law' was on his trail. He was changing his story for eventual public consumption.
According to this timeline , the inspector general had sent notice of the whistleblower complaint to Trump's Acting Director Of National Intelligence around Sep. 2. and then that individual sat on it. This timeline indicates Trump knew on Sep 9th that Congress had received notice of the whistleblower compaint about the phone call to Zelensky, in other words he chose his words to Sondland as a "cover up".
When the Republicans claim Trump said "no quid pro quo" on Sep 9th, they are knowingly or unwitingly continuing the attempted coverup. I say "attempted" because it is obvious.