President Trump posed a question Monday after a weekend of frequent tweeting about the Russia probe: Why didn't President Obama take action over Russian interference in the 2016 election?

The backdrop: The Obama administration knew about Russian efforts to interfere in the 2016 election months before Election Day, and Obama was briefed in August 2016 on intelligence that Putin himself was involved, the Washington Post reports. Still, there were limitations to what they could do, former administration officials say.

Timeline

• May 2016: James Clapper, then-director of national intelligence, issues a warning about cyber threats against the campaigns. He doesn't cite Russia.
• July 2016:
• The DNC announces it has been breached by Russian hackers. Trump says the DNC hacked itself to distract from controversies. He later invites Russia to find and release Hillary Clinton's emails.
• The FBI opens an investigation into possible collusion between the Trump campaign and the Kremlin.
• Obama, in an interview with NBC, says experts attribute the DNC hack to the Russians.
• August 2016: Obama receives top secret intelligence file detailing Putin's direct involvement in Russian election meddling.
• September 2016: U.S. intelligence agencies reach unanimous agreement regarding Russian efforts to interfere in the 2016 election.
• At a G20 meeting in Huangzhou, China, Obama pulls Putin aside and warns him directly “to cut it out."
• Clapper confirms that Russia was behind the DNC hack. Trump has by now been briefed on the matter but continues to publicly call it a hoax.
• October 2016: At Obama's direction, former Secretary of Homeland Security Jeh Johnson and former Director of National Intelligence James Clapper issue a public statement saying, “The U.S. intelligence community is confident that the Russian government directed the recent compromises of e-mails from U.S. persons and institutions, including from U.S. political organizations. We believe, based on the scope and sensitivity of these efforts, that only Russia’s senior-most officials could have authorized these activities.”
• Obama also attributes the hack of John Podesta's emails to Russia.
• December 2016: Obama approves a set of relatively modest — and primarily symbolic — sanctions, including expelling 35 Russian diplomats and closing two compounds in Maryland. The administration had considered several steeper measures including "cyberattacks on Russian infrastructure, the release of CIA-gathered material that might embarrass Putin and sanctions that officials said could 'crater' the Russian economy," per the Post.

What they're saying

• "It took time for other parts of the intelligence community to endorse the CIA’s view [on election meddling]. Only in the administration’s final weeks in office did it tell the public, in a declassified report, what officials had learned from Brennan in August — that Putin was working to elect Trump," the Post reports.
• Officials close to Obama told the Post that by August it was too late to prevent emails from being leaked, and that they believed Obama's direct warning to Putin would deter the Kremlin from taking bigger steps, such as tampering with voting systems.
• And they were concerned that any response from the U.S. would either provoke Russia to ramp up its own efforts or appear as though the administration was attempting to tip the scales for Clinton.
• But Obama was “deeply concerned and wanted as much information as fast as possible ... He wanted the entire intelligence community all over this," a former administration official told the Post.