The president is accused of dangling two things as bargaining chips to Ukraine - withholding $400m of military aid to Ukraine that had already been allocated by Congress, and a White House meeting for Ukraine's president.
This, Democrats say, amounts to an abuse of presidential power, using the office for personal political gain and to the detriment of national security. Ukraine was using that money in its ongoing conflict with Russia. Mr Trump is also accused of obstructing Congress by refusing to co-operate with the congressional inquiry.
