President Trump on Thursday called Russia's meddling in the 2016 election “all a big Dem HOAX” and accused former president Barack Obama and his administration of not doing enough last year to “stop” Russian interference.

In morning tweets, Trump opined on the Russia probe and sought to assert his innocence, even as special counsel Robert S. Mueller III expands the investigation of possible collusion between the Trump campaign and Russia to look at possible obstruction of justice by the president.

Trump tweeted, “Why did Democratic National Committee turn down the DHS offer to protect against hacks (long prior to election). It's all a big Dem HOAX!”

The president appeared to be referring to Wednesday's congressional testimony by Jeh Johnson, Obama's former homeland security secretary, who said that after the Democratic National Committee's email servers were hacked, the DNC declined an offer by the Department of Homeland Security to help the party committee, which also had been in touch with the FBI, identify intruders and patch vulnerabilities.

Former DHS chief criticizes Democratic National Committee over hacks (Reuters)

DNC officials said it did not hear from DHS until months after the hack had been made public and after the FBI had worked to close the intrusion, and that the DNC provided the DHS a detailed report on the incident.

“The DNC has and will continue to cooperate with law enforcement on Russia's interference in our election,” DNC spokeswoman Adrienne Watson said in a statement responding to Trump's tweet. “The DNC has been in regular contact with the FBI for many months and the FBI confirmed the DNC has provided all the information it needed to make its assessment.”

In another Thursday tweet, Trump wrote, “If Russia was working so hard on the 2016 Election, it all took place during the Obama Admin. Why didn't they stop them?”

Josh Earnest, Obama's former White House press secretary, responded to Trump's tweet in an appearance on MSNBC. Noting that Russia's overall goal was to shake confidence in the United States' ability to have an election, Earnest said it would have been “irresponsible” for the administration to have taken more active public steps expressing worry about Russia's actions.

“We wanted to make sure that we were instilling confidence in people that we could conduct a free and fair election,” Earnest said.

Trump used the caveat of “if Russia was working so hard,” making clear that he is not yet convinced that Russia interfered in the election with its cyberattacks and other activities.

Sixteen U.S. intelligence agencies have concluded that Russia did in fact meddle in the election, through cyberattacks and other activities, with the explicit aim of influencing the outcome. White House press secretary Sean Spicer told reporters Tuesday that he did not know whether the president believed the conclusion of his own intelligence agencies.

In a third tweet Thursday, Trump sought to use Johnson's testimony as proof of his vindication in the Russia investigation. “Former Homeland Security Advisor Jeh Johnson is latest top intelligence official to state there was no grand scheme between Trump & Russia,” the president tweeted.

Yet Johnson is not involved in Mueller's expanding federal investigation into Russian interference and therefore would not have the knowledge or authority to exonerate Trump. The Washington Post reported last week that Mueller was investigating Trump for possible obstruction of justice, as well as probing Russia's activities to influence the election and whether there was any collusion between Russia and Trump's campaign.

In testimony Wednesday before the House Select Committee on Intelligence, Johnson said that Russia's meddling, directed by Russian President Vladimir Putin, was “unprecedented” in scale and scope.