Who is the biggest threat to our constitutional order? It is not President Trump.

Ever since Trump took office, Democrats have been telling us he is an authoritarian who threatens our system of government. Well, today it is Democrats who are declaring war on the Constitution. Leading Democrats are promising that, if elected in 2020, they will abolish the Electoral College and might also pack the Supreme Court with liberal justices -- allowing them to marginalize Americans who do not support their increasingly radical agenda and impose it on an unwilling nation.

The purpose of the Electoral College is to protect us from what James Madison called the "tyranny of the majority." Each state gets to cast electoral votes equal to the combined number of its U.S. representatives (determined by population) and its senators (two regardless of population). The goal was to make sure even the smallest states have a say in electing the president and prevent those with large, big-city populations from dictating to the less populous rural ones.

MARC THIESSEN: DEMOCRATS APPARENTLY LIKE LOSERS. WE'LL SOON SEE IF ONE CAN WIN THE PRESIDENCY IN 2020

No wonder Democrats don't like it. Today, they have become the party of big-city elites, while their support is declining in less populous states of Middle America. Just look at a county-by-county map of the 2016 election -- you can actually drive from coast to coast without driving through a single county that voted for Hillary Clinton. Clinton lost in 2016 because millions of once-reliable Democratic working-class voters in the American heartland switched their allegiance to Trump.

Thanks to the Electoral College, Democrats have no choice but to try to win at least some of those voters back if they want to win the presidency. But if we got rid of the Electoral College, Democrats could write off voters in "fly-over" country and focus on turning out large numbers of their supporters in big cities and populous liberal states such as New York and California. Unburdened by the need to moderate their platform to appeal to centrist voters, they would be free to pursue full socialism without constraint. If voters in Ohio, Michigan, Wisconsin and Pennsylvania oppose spending tens of trillions on a Green New Deal and a government take-over of the health care, energy and transportation sectors of the economy, tough luck.

The Electoral College protects us from this kind of unconstrained radicalism, by forcing the political parties to broaden their appeal -- which is precisely why more and more Democrats want to get rid of it. Fortunately, the framers of the Constitution required supermajorities for amendments -- another wise protection against the tyranny of the majority.

But Democrats would have no such obstacles in dealing with another impediment to their radical agenda: the Supreme Court. Thanks to Trump's Electoral College victory, Republicans have been able confirm two Supreme Court justices and secure a conservative majority. Democrats have no one but themselves to blame for their judicial predicament. They were the ones who announced that they would not confirm a Supreme Court justice during George W. Bush's final year in office, setting the precedent for Republicans to block President Barack Obama's nomination of Merrick Garland. And they were the ones who eliminated the filibuster for federal circuit courts judges -- setting the precedent for Republicans to eliminate the filibuster for Supreme Court justices.

Democrats have miscalculated at every turn, and now their solution is to break precedent yet again -- by packing the Supreme Court. There have been nine justices on the Supreme Court for the past 150 years. No matter, Democratic candidates including Elizabeth Warren, Kamala Harris, Kirsten Gillibrand, Pete Buttigieg and Beto O'Rourke have all said that, as president, they would consider adding justices to the Supreme Court to secure a left-wing majority. The last president who tried this, Franklin D. Roosevelt, was stopped only because members of his own party rebelled. The Senate Judiciary Committee, then controlled by the Democrats, correctly declared his plan "an invasion of judicial power such as has never before been attempted in this country."

CLICK HERE TO GET THE FOX NEWS APP

It seems unlikely a Democratic president would face such a rebellion today. But unless Democrats win not only the presidency but also a 60-vote Senate majority, they would have to eliminate another minority protection -- the legislative filibuster -- to pass a court-packing bill. I suspect they would not hesitate to do so.

Taken together, the Democrats are proposing what amounts to a systemic assault on the foundations of our federal system. Democrats are freely pursuing a tyranny of the majority. We'll see how it plays in Middle America. But if they do, then spare us the overwrought complaints about Trump. You can't defend the Constitution while trying to tear it up at the same time.

CLICK HERE TO READ MORE FROM MARC THIESSEN