The Constitution calls for three separate and coequal branches of government, each operating independently of each other, and each with their own powers—and limitations. But in recent years, under both Republicans and Democrats, the federal government has acted more like an entity made of just two branches, or possibly two and a half. Congress has abdicated much of its responsibility for legislating, descending into petty dysfunction when power is divided and acting more like a subservient arm of the executive when one party controls both the White House and the Capitol.

One result is that the executive branch has grown stronger, ruling by regulations and executive orders rather than laws debated and passed by those elected to do so. Another is that the system of checks and balances designed to provide oversight and accountability to all three branches has effectively lost one of its checks, leaving the entire system in a precarious state of imbalance. That imbalance is on display today in the wake of President Trump's highly suspicious firing of FBI Director James Comey.

Under Trump, Republicans have resisted providing meaningful oversight of the executive branch. Consider Rep. Jason Chaffetz, the Republican head of the House Oversight Committee.

A month before last year's presidential election, when most observers expected Hillary Clinton to win the presidency, he announced that he had two years of investigations already in the pipeline.

Yet once Trump was elected, Chaffetz's desire to investigate the White House mysteriously vanished. At the end of January, Chaffetz released a 43-point list of issues he planned to investigate, not one of which related to Trump. The following month, Chaffetz said that his committee would not investigate Trump adviser Michael Flynn, who resigned as Trump's national security adviser amid questions about contacts with Russian officials. In April, he rather unexpectedly announced that he would not run for reelection in 2018, and would be taking immediate medical leave.

Chaffetz, a rising star in the Republican party who looked forward to years of oversight of a Hillary Clinton administration, had lost his appetite for the job. He did, however, seem to regain that appetite briefly last week when he announced that he would investigate presidential pension payments—made to President Barack Obama.

So it is hardly surprising that following the firing of FBI Director James Comey, which Trump justified with reasoning that is contradictory and difficult to believe, Mitch McConnell, the top Republican in the Senate, responded by dismissing calls for a special prosecutor to investigate the president. A few Republicans, including Rep. Justin Amash and Sen. John McCain, have expressed support for an outside investigation, but Republicans have largely backed the president on the firing. And McConnell rejected the idea of additional congressional oversight. "Today we'll no doubt hear calls for a new investigation," he said in a speech this morning, "which can only serve to impede the current work being done."

McConnell's statement is not only cynical. It is detrimental to his own institution, the Senate, and to the American system of government. It does not portend a constitutional crisis, yet. But it does suggest a willingness to continue to slouch into constitutional weakness and dysfunction.

McConnell is effectively arguing that an independent investigation should not be pursued because it would bog down the legislative agenda of President Trump and the Republican party. It is an argument that Congress should not play its constitutional role, but should instead function as a partisan lackey operation for the executive branch. That is a worrying view under any president. Under a self-dealing president with sketchy affiliations such as Trump, it is even more dangerous.