(CNN) Republicans are struggling to find a unified defense as they shift their ever-changing arguments about why President Donald Trump's actions are not impeachable, amid damaging testimony from senior diplomats that Trump sought to condition US military aid to Ukraine on opening investigations into his political rivals.

What once was a frequently repeated mantra -- there was no quid pro quo -- has now morphed into a multi-pronged and sometimes disjointed defense, with Republicans each taking the job into their own hands, hoping to fight back against the allegations raised daily with the release of new transcripts.

Republicans across the Capitol have resorted to attacking the firsthand knowledge of witnesses, muddying the waters with calls to name the whistleblower and even seeking to discredit the Trump administration's ability to be organized enough to execute a scheme to use military aid in order to advance its own political agenda.

"What I can tell you about the Trump policy toward Ukraine: It was incoherent, it depends on who you talk to, they seem to be incapable of forming a quid pro quo, so no I find the whole process to be a sham and I'm not going to legitimize it," Senate Judiciary Chairman Lindsey Graham, a South Carolina Republican, told reporters Wednesday.

The shifting strategy comes as a tidal wave of new information emerges from transcripts of key witnesses including US Ambassador to the European Union Gordon Sondland, who surprised lawmakers by amending his testimony and who made things more complicated for Republicans.

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