From your link:
The United States should join scores of other nations, including Germany and France, and create a specialized court to decide constitutional questions.
That is what the Supreme Court is designed to do.
About the Supreme Court
Quote: Therefore, the Court has the final say over when a right is protected by the Constitution or when a Constitutional right is violated.
The Supreme Court plays a very important role in our constitutional system of government. First, as the highest court in the land, it is the court of last resort for those looking for justice. Second, due to its power of judicial review, it plays an essential role in ensuring that each branch of government recognizes the limits of its own power. Third, it protects civil rights and liberties by striking down laws that violate the Constitution. Finally, it sets appropriate limits on democratic government by ensuring that popular majorities cannot pass laws that harm and/or take undue advantage of unpopular minorities. In essence, it serves to ensure that the changing views of a majority do not undermine the fundamental values common to all Americans, i.e., freedom of speech, freedom of religion, and due process of law.
The Democrats are supporting changing that when they become the majority and can impose their will. Removing the Supreme Courts ability to set limits, removes that protection.
This is just a power grab - plain and simple. The Democrats cannot get their agenda through the legislature, so they are attempting to change the rules.