The most surprising thing about Comey’s testimony

• James Comey's testimony on Thursday before the Senate was riveting.
• The most surprising part wasn't Comey's testimony but how lawmakers responded.
• Perhaps the most disturbing thing is that President Trump, in his effort to call off the Flynn investigation, demonstrated a profound indifference to the rule of law.

Viewers across the country expected riveting television from today's Senate Intelligence Committee hearing, and the star witness, former FBI director James Comey, delivered. His testimony contained few actual surprises — most of it was previewed in his written remarks, which were themselves foreshadowed by news reports. But it still painted a lurid picture of a United States president pressuring the FBI director to declare his loyalty, and to prove it by dropping the FBI's investigation into the president's former aide.

What was surprising was not so much what Comey said, but how lawmakers responded. Members of both parties duly fretted over Russia's interference in the 2016 election. When it came to the Trump campaign's possible role in that interference, though, there was little discussion. And Trump's defenders on the committee did their best to downplay the president's attempt to interfere with the FBI's investigation. In a committee that is generally marked by rare bipartisanship, the partisan divide was on stark display.

The rule of law, however, should never be a partisan issue. Although senators questioned Comey closely on his response to Trump's inappropriate comments, they did not question his version of events. They seemed to accept that Trump made the statements Comey attributed to him —namely, that he hoped Comey would "let go" of the investigation into former National Security Adviser Michael Flynn. At that point, all partisanship should have receded, and the committee should have been unanimous in its condemnation. A president asking the FBI investigator to drop an investigation into the president's associate is a clear-cut case of obstruction of justice.

Some committee members tried to avoid this conclusion by suggesting that Trump was merely expressing an idle wish that the investigation would end, rather than asking Comey to end it. As defenses go, this one is laughable. The president began the meeting by asking Comey if he wanted to keep his job. In the same discussion, he said, "I hope you can see your way clear to letting this go, to letting Flynn go." There is nothing subtle in this juxtaposition. When the boss asks if you wants to keep your job and then tells you what he "hopes" you will do, you get the message. And when you fail to honor his "hopes" and get fired — well, that clears up any lingering ambiguity.

Other members emphasized Comey's own sense that Trump was not asking him to shut down the entire Russia investigation — just the inquiry into Flynn's involvement. Even if true, that would still mean Trump attempted to obstruct justice, just on a smaller scale. It is a sad day for the president's supporters when they have to fall back on the argument that he could have chosen to interfere with a criminal investigation even more aggressively than he did.

The president's effort to call off the Flynn investigation is disturbing for another reason: It is evidence of his profound indifference to the rule of law. Some have suggested that Trump may not have known his behavior was inappropriate, and it was up to Comey to educate him. This notion should set off immediate alarm bells. Ignorance of the law is no defense, and ignorance of the rule of law, in a president, is terrifying. Dictators put their enemies in jail and keep their friends out. Presidents don't — and they should come into office knowing that.

Trump's transgression cannot be shrugged off as an innocuous attempt to help someone Trump described as a "good guy." If Trump felt that Flynn was a decent individual who did not deserve to be prosecuted, the Constitution gives him a legal way to accomplish this goal: He could exercise his pardon power. But that power must be exercised openly, so that there is a political check on its misuse.

In any event, it is far from clear that the investigation into Flynn and the larger Russia investigation can neatly be separated. After all, Trump grudgingly fired Flynn (and then complained about his unfair treatment) because Flynn lied about conversations with Russian ambassador Sergey Kislyak. In those conversations, Flynn engaged in improper discussions of the sanctions the U.S. had placed on Russia — sanctions the Trump administration is now in the process of rolling back. Flynn was a paid contributor to a Russia-owned news station, although he did not comply with his legal obligation to disclose these payments. He had extensive business ties with Russian firms and was seated next to Vladmir Putin at a gala in Moscow.

In short, it seems quite likely that Flynn is a critical figure in the larger investigation into collusion between the Trump campaign and Russia. And it is possible that Trump himself knows more about Flynn's involvement with Russian interests than the FBI does. Cutting Flynn out of the picture could potentially have a significant effect on how the investigation proceeds.

Members of Congress, regardless of party, should uniformly support the investigation into Russia's interference with the election, including any possible involvement by Trump campaign officials. There is no matter more important to our democracy and our security. If the president tried to shut down any part of this investigation — and the evidence strongly suggests he did — Congress should view this as a call to ramp up its own investigative efforts.

Those efforts should not stop at the narrow questions we heard today. Congress's jurisdiction is much broader than that of the special counsel. Regardless of whether a crime was committed, Congress should find out what conditions enabled the Russians to get a foothold in our election, and what can be done to protect ourselves in the future. And Congress should demand a full accounting of the nature and extent of the ties between Trump administration officials and the Russian government or other close Putin allies. If, in fact, the president and much of his inner circle are indebted — whether financially or otherwise — to a hostile foreign power, it is vital for lawmakers and the public to have that information.

The Comey show is over for now, but there is a tremendous amount of work to be done. Americans must call on their representatives to move forward with this work, and to do so with their eyes firmly fixed on the greater good of the country. We can defeat the forces that are working to undermine our democracy, but to do so, we must defeat partisanship first.

Commentary by Elizabeth (Liza) Goitein, the co-director of the Brennan Center's Liberty and National Security Program at New York University's School of Law. She focuses on a range of issues at the intersection of national security policy and civil liberties, including the oversight mechanisms in place for intelligence activities. She has written about the implications of Comey's firing and the need for a robust congressional investigation, and has previewed Comey's testimony in various outlets. Follow her on Twitter @LizaGoitein.

For more insight from CNBC contributors, follow @CNBCopinion on Twitter.