https://www.justsecurity.org/66705/united-states-of-america-v-rudolph-w-giuliani/
"An individual who conspires to inject foreign interference into a U.S. election attacks the very heart of democracy. Our laws prohibit foreign influence in our elections because our founding fathers believed that only American citizens should decide who holds public office in the United States, and we recognize that foreign governments and their citizens act in their own interests, not ours. Criminal cases are prosecuted for several reasons, including deterring illegal conduct, promoting respect for the rule of law, and protecting public safety. A prosecution here would advance all of these important goals. A few observations on the charge for contempt of Congress deserve mention. Giuliani’s refusal to comply with a subpoena for documents, which was issued by the three House Committees conducting the impeachment inquiry, is a criminal offense. In a letter to the Committees, Giuliani stated that he would not comply with the subpoena because it is part of an “unconstitutional, baseless and illegitimate ‘impeachment inquiry.'” Witnesses may challenge the scope of a subpoena as harassing, oppressive or overly broad by filing a motion to quash in court. They may not simply ignore the subpoena and defy Congress’s authority as one of three co-equal branches of government. The Constitution gives the power of impeachment to the House, and allows it to fashion its own rules for handling impeachment. There is no requirement that the full House take a vote before it may begin an impeachment inquiry, and the House has the authority to investigate any matter on which it may act, including impeachment. Giuliani’s conduct violates the federal criminal statute prohibiting witnesses from defying subpoenas issued by Congress or its committees. A subpoenaed witness before Congress can no more ignore a subpoena than can a witness in a federal trial."
