This comic is spot on. As detailed in this article published by NPR, Donald Trump first claimed that the reason he blocked critical aid to Ukraine was because of concerns over corruption in that country. However, the Department of Defense back in May (before Trump blocked the aid in July) “certified that the Government of Ukraine has taken substantial actions to make defense institutional reforms for the purposes of decreasing corruption [and] increasing accountability.”
Trump then changed his tune, and claimed that he was concerned that the US was the only country contributing aid to Ukraine, saying “Europe and other nations [must] contribute to Ukraine. Because they’re not doing it. Just the United States. We’re putting up the bulk of the money.” This (of course) is a pure fabrication.
Trump has never asked European countries to increase their aid to Ukraine. And you know why? Because Europe is already contributing more money to the Ukraine than the US is.
So why did Trump withhold the critical aid to Ukraine? Remember that Trump asked the new president of Ukraine eight times to investigate Biden and his son Hunter. After initially denying this, Trump later admitted that he had asked them to investigate the Bidens, but said that there was nothing wrong with doing that. When then led to the string of excuses that Trump has made up about this.
Also remember that the Bidens had already been investigated about their activities in Ukraine, and cleared of any wrongdoing. And Trump (or anyone else) has never presented any evidence to the contrary. So this was purely political. Trump was asking a foreign government to interfere in a US election. That is against the law. At least one Republican is calling it treason.