The story is that Trump may have been pressuring Ukraine by using monetary and military support as leverage. This concern was previously raised when Ukraine suddenly stopped cooperating with the Mueller investigation in order to avoid angering Trump. Whatever the case may be, the ICIG made a determination that the conduct described by the whistle-blower was a serious and urgent matter that, under the circumstances, strongly raises the suspicion of criminality—a senior intelligence officer is unlikely to have made such a complaint about Trump doing something that is within his powers.