Russian President Vladimir Putin (Alexei Nikolsky/AP)

As Russia stepped up its propaganda campaign during the 2016 presidential election, U.S. intelligence and law enforcement agencies saw some warning signs, but never fully grasped the full scope of the Kremlin's ambitions, The Washington Post reported Tuesday.

Top U.S. policymakers eventually ended up scrambling on how to fight back, though plans ultimately "died of internal disagreement, a fear of making matters worse or a misguided belief in the resilience of American society and its democratic institutions," according to the report.

In one case, a "sweeping" presidential finding to combat global cyberthreats, led U.S. spy agencies to "plan a half-dozen specific operations to counter the Russian threat."

However, a year later, the Trump White House "remains divided over whether to act," intelligence officials told the Post.

"I thought our ground was not as fertile," said Antony Blinken, a deputy secretary of state in the Obama administration. "We believed that the truth shall set you free, that the truth would prevail.

"That proved a bit naive."

The Post said that its report was based on "interviews with dozens of current and former senior U.S. officials at the White House, the Pentagon, the State Department, and U.S. and European intelligence services, as well as NATO representatives and top European diplomats."

President Donald Trump has continued to slam the idea of Russian interference in last year's election, calling the investigation by special counsel Robert Mueller a "witch hunt."

Other Trump allies also contend that Democrats are using Moscow to delegitimize the president's election victory.

"If it changed one electoral vote, you tell me," one senior administration official told the Post.

The official requested anonymity.

"The Russians didn't tell Hillary Clinton not to campaign in Wisconsin," the official said. "Tell me how many votes the Russians changed in Macomb County [in Michigan].

"The president is right: The Democrats are using the report to delegitimize the presidency."

But other senior White House officials, as well intelligence officials, do not question Moscow's role in the election.

"We should have every expectation that what we witnessed last year is not a one-shot deal," Douglas Lute, the former U.S. ambassador to NATO, told the Post. "The Russians are onto something.

"They found a weakness," Lute added, "and they will be back in 2018 and 2020 with a more sophisticated and targeted approach."