United States senators do not serve the president — at least, that’s not the way James Madison envisioned it. Congress has a broad range of tools it can use to rein in the power of an out of control president and defend constitutional democracy.

The problem is that members of Congress have to be willing and able to exercise their power and fulfill their responsibilities. Otherwise, in Madison’s words, the authority assigned and entrusted to them by the Constitution, becomes mere “parchment barriers” — empty words on paper.

Senate Majority Leader Mitch McConnell (R-KY) is proving the wisdom of Madison’s warning.

McConnell may, as historian Christopher Browning puts it, be seen by future generations as having been the “gravedigger of American democracy”. At every turn, McConnell has prioritized loyalty to President Donald Trump over loyalty to constitutional democracy — whether by blocking public revelation of Russia’s attack on the 2016 election, declining to protect the Mueller investigation, or refusing to back legislation to end the government shutdown unless it has the president’s support. It is not hyperbolic to say that, without Mitch McConnell, there might well be no Trump presidency.

Read: Stock market could feel drag from shutdown by next week, analysts warn

“ If Trump were an ordinary president, McConnell’s deferential enabling would not threaten the foundations of American democracy. ”

If Trump were an ordinary president, McConnell’s deferential enabling would not threaten the foundations of American democracy. But Trump has made clear he does not respect the rule of law. Several members of his inner circle, including his former lawyer, first national security advisor, and former campaign chairman, are now convicted felons. Every week (sometimes every day) brings new, troubling information about Trump’s legal peril and possible compromise by Russian President Vladimir Putin.

A recent profile in the New York Times suggests that McConnell understands at least some of the danger associated with Trump’s presidency. When an interviewer asked McConnell whether he worried about enabling a president who “seem[s], in some ways, very much inclined to do damage to institutions of American governance”, the majority leader did not dismiss the premise of the question. Instead of denying that the president is a threat to government institutions, McConnell responded that “the ultimate check against any of this is the ballot box.” He went on to suggest that last year’s midterm elections in the House of Representatives showed that “there were plenty of people who wanted a midcourse correction.”

“ McConnell seems to think of himself as merely a spectator when it comes to setting limits on President Trump. ”

That’s a revealing statement. McConnell appears to be sympathetic to the idea that the president — the leader of the Republican Party — is someone who needs to be checked. Of course, no president should operate outside of the constitutional system of checks and balances, but in recent American history, it is hard to imagine a congressional leader endorsing or at least condoning the idea that a president of his or her own party needs reining in. At the same time, McConnell seems to think of himself as merely a spectator when it comes to setting limits on President Trump. That could well be a mistake, for two reasons.

First, the Times profile reports that McConnell’s friends and allies consistently describe him as a “student of history.” How will history judge McConnell’s passive bystander approach when it comes to Trump’s dangerous presidency? As the historian Browning suggests, McConnell may ultimately be seen as someone who enabled a would-be authoritarian.

Second, McConnell may have to worry about his own political consequences. He will stand for re-election in 2020, after completing his sixth term in office. The majority leader is walking a fine line. In order to avoid or withstand apossible primary challenge in Kentucky, a state where Trump’s approval rating stood at 55% - 40% as of December 2018, McConnell will want to avoid crossing the president. That, of course, may explain his failure to stand up to Trump.

In the general election, McConnell’s ties to Trump could prompt a serious Democratic challenger to take on the majority leader. Recent polling found McConnell to be the third-most unpopular member of the U.S. Senate. The only two senators in that poll less-popular than McConnell: Jeff Flake (R-AZ) and Claire McCaskill (D-MO), who are no longer in the senate.

Over the next two years, it will be worth watching to see how far McConnell goes in playing courtier to Trump. As of now, polling shows Americans blame the president for the partial government shutdown. So far, McConnell has said that he can only support legislation the president will accept, incorrectly claiming that “what you need in order to make a law is the presidential signature.” If the shutdown continues, McConnell could be blamed, especially if the standoff continues to roil financial markets. McConnell could also face unwelcome scrutiny if he stands in the way of holding Trump accountable for malfeasance associated with the Mueller investigation.

If it becomes clear that there are enough votes in the senate to re-open the government over Trump’s veto, blame could fall on McConnell — especially if the shutdown continues to roil financial markets. McConnell could also face unwelcome scrutiny if he stands in the way of holding Trump accountable for malfeasance associated with the Mueller investigation.

As he thinks about the 2020 election and his own political future, McConnell will continue to face the challenge of walking a tightrope when it comes to the Trump presidency. The majority leader may be interested in the verdict of future historians, but a more immediate concern may be the judgment of Kentucky voters.

Chris Edelson is an assistant professor of government in American University’s School of Public Affairs. His book, “Power Without Constraint: The Post 9/11 Presidency and National Security,” was published in 2016 by the University of Wisconsin Press.