One of the Republican defenses against a possible quid-pro-quo is that Zelinsky did not feel any pressure. We know this because he said he did not feel pressure. But, why do we believe this statement of his? Of course he felt pressure - the President of the United States, one of the most powerful countries in the world was asking him to do something. If he gets on the US's bad side, it could be very bad for him. The US gives Ukraine tons of money in military aid - besides for any other positive effects that may result from having a world super power on your side. So, why do we take Zelensky's word when he says he wasn't pressured?
Republicans are taking the role of Trump's defense, not judges, or investigators.
One of their bigger problems is that they have no defense witnesses. Everyone who could give testimony that supports one of the many defenses offered has been forbidden by the Trump administration from testifying, or been dismissed as irrelevant by the Democrats.
Because they have no witnesses, they need to get whatever they can. A statement by the president of the Ukraine that he didn't feel pressured is better than nothing.
Democrats have specifically countered that defense through witness testimony (warning: autoplay video!) that contradicts Zelensky - who did not speak under oath, had reasons to avoid antagonizing Trump, and whose words may have been mistranslated.
So, why do we take Zelensky's word when he says he wasn't pressured?
The Democrats in the House Intelligence Committee don't say that; they claim he was pressured.
Their report describes the pressure put on Ukraine repeatedly, based on testimony and evidence. I will quote directly from the report (emphasis mine; selective quotes, see report for full context):
In his public testimony, Ambassador Sondland testified that the President’s direction to withhold a presidential telephone call and a White House meeting for President Zelensky were both quid pro quos designed to pressure Ukraine to announce the investigations.
On October 17, at a press briefing in the White House, Acting Chief of Staff Mick Mulvaney confirmed that President Trump withheld the essential military aid for Ukraine as leverage to pressure Ukraine to investigate the conspiracy theory that Ukraine had interfered in the 2016 U.S. election.
In their key findings of fact, which shows how the report characterizes the efforts as pressure.
II In furtherance of this scheme, President Trump—directly and acting through his agents within and outside the U.S. government—sought to pressure and induce Ukraine’s newly-elected president, Volodymyr Zelensky, to publicly announce unfounded investigations that would benefit President Trump’s personal political interests and reelection effort.
V President Trump used the power of the Office of the President and exercised his authority over the Executive Branch, including his control of the instruments of the federal government, to apply increasing pressure on the President of Ukraine and the Ukrainian government to announce the politically-motivated investigations desired by President Trump.
VI (...) In fact, the President sought to pressure and induce the government of Ukraine to announce politically-motivated investigations lacking legitimate predication that the U.S. government otherwise discourages and opposes as a matter of policy in that country and around the world.
Finally, they had a witness, Mr. Holmes, testify the Ukrainians did feel the pressure. Again from the report:
By the time of the inauguration, Mr. Holmes assessed that President Zelensky and the Ukrainians were already starting to feel pressure to conduct political investigations related to former Vice President Biden.