From the summary section: "In general, the Senate's presiding officer does not take the initiative in enforcing Senate rules and precedents. Instead, a Senator may raise a point of order if he or she believes the Senate is taking (or is about to take) an action that violates the rules. In most circumstances, the presiding officer rules on the point of order on advice of the Parliamentarian; that ruling is typically subject to an appeal on which the Senate votes (unless the appeal is tabled or withdrawn). Pursuant to Rule XX, however, in certain circumstances a point of order is not ruled on by the presiding officer but is instead submitted to the Senate for its decision. A point of order that a pending matter (a bill or amendment, for example) violates the U.S. Constitution presents one such circumstance. This report explains Senate rules, precedents, and practices in regard to these constitutional points of order, including an analysis of recent cases in which such a point of order has been raised, and will be updated as events warrant. […] This report identifies 17 constitutional points of order that have been raised and received a Senate vote since 1989. Eleven of these cases were disposed of negatively."
CRS Report for Congress, R40948