Julian Zelizer is a professor of history and public affairs at Princeton University, and author, with Kevin Kruse, of the new book " Fault Lines: A History of the United States Since 1974. " Follow him on Twitter at @julianzelizer. The opinions expressed in this commentary are his own. View more opinion at CNN.

(CNN) Last weekend, Democrats lost control of the political narrative to President Donald Trump and the Republicans. And they will have to work quickly if they want to get it back.

It went like this: When reporters learned that special counsel Robert Mueller had submitted the results of his inquiry into Russian interference in the 2016 election, and would not be issuing any more indictments, Republicans crowed that it was a victory for Trump.

And on late Sunday afternoon, Attorney General William Barr finally released his report summary, which acknowledged that Mueller had not exonerated the President of obstruction of justice, and the Republican celebration continued.

Trump went into overdrive, called his opponents "treasonous" and said there would be investigations into how this all unfolded. He pointed to Barr's revelation that Mueller had not established "that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities."

Even though nobody other than the attorney general and deputy attorney general has seen the report, newspaper headlines, website banners and television chyrons -- along with Trump's Republican colleagues -- immediately echoed his version.

But spin is what it was.

The entire episode was a lesson for Democrats about how good Trump and the Republican Party can be -- when they put their minds to it -- at swaying the political narrative in the era of 24-hour, instantaneous news. One thing Democrats are up against, of course, is a President willing to say almost anything to shape the news cycle in a way that he wants.

It is a dazzling act, when one considers the many questions the Barr letter leaves on the table.

Foremost, the attorney general confirmed that the Russians did intervene in the 2016 election, a claim that Trump has often been hesitant to make or has denied. Second, the summary of Mueller's findings doesn't tell us anything about what evidence the special counsel did collect and what all the Russia contacts -- and lies to hide the contacts by top-level officials -- were about.

Finally, Barr wrote that Mueller did not make a final determination about whether the President had obstructed justice and left that to others to decide. Mueller would not exonerate him. Why wouldn't he?

Democrats have much to work with here. The good news for them is that Trump may be good at spinning the news, but it often bounces back on him and his party. Indeed, the same day that Democrats were reeling from Trump's victory lap, the Justice Department announced it is moving to strike down the entire Affordable Care Act, which would leave millions of Americans without their health care and millions more exposed to poor insurance.

This move quickly offered Democrats a reminder of how they can push the national conversation in a direction that would benefit them: public policy.

Outside of very red districts in conservative states, large portions of the population stand by the party of FDR. Keeping the national spotlight on policy-based conversation, rather than Trumpian chaos, will likely help Democrats gain ground.

With their base in the House, Democrats can also offer an alternative against Trump's everything-has-gone-my-way story by continuing their serious oversight investigations into the White House.

Rather than closing up shop for fear that they would reignite the political backlash Republicans faced in the late 1990s after they impeached President Bill Clinton, Democrats today would benefit by continuing to ask hard questions. They can legislate and investigate at the same time.

From answering what appears to be Mueller's open-ended question about obstruction of justice to looking into Trump's ongoing potential conflict-of-interest issues, to probing alleged criminal activity within the campaign, congressional Democrats can make sure that Americans don't lose sight of the striking evidence before their very eyes. It has pointed to broader patterns of unethical activity and possible abuse of power that would make Richard Nixon blush.

To regain control of the national conversation and stay clear of Trump spin, the slate of Democratic presidential candidates, along with House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer, will also need the discipline to react less to the President.

Trump's most potent weapon is his ability to trigger America's political class. He makes it difficult to bring up any issues or any debates outside the framework he establishes through his Twitter feed: His tweets quickly swamp entire news cycles.

And that's what happened this weekend with the Barr letter. But Democrats don't have to play along.

They need to look to some of the younger voices in the party, such as Rep. Alexandria Ocasio-Cortez, who have proven through inspirational speeches and shrewd social media tactics how to edge Trump out of his airtime.

Democrats need to take a lesson from newly energized Republicans. Rather than spending the next few weeks sulking and apologizing, they need to stay out front of the news, taking steps to make sure that their issues are part of the discussion and that the great risks posed by the President never fade from the public eye.