American Confidence in Elections Act or the ACE Act This bill addresses election administration and security, campaign finance, and other related provisions. Specifically, the bill directs the Election Assistance Commission's (EAC's) Standards Board and Local Leadership Council to issue voluntary considerations for states about various aspects of election administration. Additionally, the bill reduces certain election assistance payments for states and local jurisdictions that allow noncitizens to vote; requires states to provide designated congressional election observers with full access to observe the administration procedures of federal elections; prohibits federal agencies from using funds made available for salaries and expenses to solicit or enter into agreements with nongovernmental organizations to conduct voter registration or voter mobilization activities on the agency's property or website; prohibits federal funds for election administration for states that allow ballot harvesting, with exceptions; establishes various requirements for elections in the District of Columbia; makes various changes to the EAC; and prohibits foreign nationals from making contributions or donations in connection with state or local ballot initiatives or referenda. The bill also establishes the Twentieth Amendment Section Four Panel, which must recommend to Congress model legislation to resolve any vacancy created by the death of a candidate in a contingent presidential or vice-presidential election. The bill makes changes to campaign finance, including by (1) repealing limits on coordinated party expenditures, and (2) prohibiting federal funds from being used to make payments in support of a congressional election campaign. It also makes changes to the Federal Election Commission.