He wasn't impeached for denying foreign aid, he was impeached for making the aid conditional on helping him personally in his campaign for re-election. A fairly obvious case of corruption.

"Using the powers of his high office, President Trump solicited the interference of a foreign government, Ukraine, in the 2020 United States Presidential election. He did so through a scheme or course of conduct that included soliciting the Government of Ukraine to publicly announce investigations that would benefit his reelection, harm the election prospects of a political opponent, and influence the 2020 United States Presidential election to his advantage. President Trump also sought to pressure the Government of Ukraine to take these steps by conditioning official United States Government acts of significant value to Ukraine on its public announcement of the investigations."