As a former ambassador to Ukraine under Bush the younger 2006-2009, William "Bill" Taylor wrestled for the country and wanted to help US-Ukraine relations.

Yesterday, the respected diplomat sat and read a 15-page testimony that - on paper - could destroy a presidency. Now, it was not an anonymous whistleblower with secondhand information that said the president was withholding military aid until he had the President of Ukraine openly declare that he would investigate the Biden family.

Confirms what the whistleblower says

Now it was the US ambassador to the country who described how he slowly but surely understood that there were not one, but two, channels communicating with Ukraine. An official, and an unofficial, led by Trump's personal lawyer Rudy Giuliani. In short: Bill Taylor confirms what the whistleblower says.

President Trump did not want to give Ukraine money until he had an official comment to investigate Biden. For Democrats, this is a "slam dunk". They have the president in a vice, with a reliable witness, hand-picked to his office by Trump's own Secretary of State Mike Pompeo.

But Republicans interpret it differently. And the limit of what is acceptable to a president continues to stretch. When the first whistleblower emerged, Republicans said it was only secondary information and could not be trusted. When the second whistleblower came forward, with first-hand information, Republicans said there was no evidence of blackmail, so-called quid pro quo.

The testimony continues

When Bill Taylor testified yesterday that it was in fact a withholding of money until Trump got what he wanted, well then the boundaries were moved again. Today, the Republican argument is that a quid pro quo is a "natural part of the president's negotiations" as long as it is about the country's best and not its own gain. And the former, they say, is the case here. That the Trump administration was concerned about corruption in Ukraine and wanted to be sure the money was in the right hands.

The testimony continues for a few weeks. It remains to be seen what additional boundaries will be stretched. A diplomat under oath, testifying to the president's personal pressure, is not enough.