Watch: Trump slams $1.3 trillion spending bill but says he signed it

A visibly annoyed President Donald Trump faced reporters at the White House on Friday.

Trump tweeted shortly before the briefing that a 1 p.m. "news conference" will address the omnibus spending bill that he threatened to veto earlier in the day. The White House said it the event would be a "press availability" featuring the president.

Trump tweet News conference at the White House concerning the Omnibus Spending Bill. 1:00 P.M.

Trump said he signed the bill, despite his unhappiness with it, because of national security concerns.

Trump sent shockwaves through Congress when he made the threat to reject t $1.3 billion spending bill after it passed the Senate late last night with bipartisan support.

Trump tweet I am considering a VETO of the Omnibus Spending Bill based on the fact that the 800,000 plus DACA recipients have been totally abandoned by the Democrats (not even mentioned in Bill) and the BORDER WALL, which is desperately needed for our National Defense, is not fully funded.

If the 2,000-plus-page omnibus spending package — which was rammed through the legislature less than two days after it was available to read — is not signed into law by 12:01 a.m. Saturday, it will trigger a government shutdown.

The briefing arrives amid an especially turbulent week for the administration, which involved multiple high-level resignations and the recrudescent threat of a government shutdown.

On Thursday, Trump confirmed the resignation of national security advisor Gen. H.R. McMaster in a tweet.

Trump tweet I am pleased to announce that, effective 4/9/18, @AmbJohnBolton will be my new National Security Advisor. I am very thankful for the service of General H.R. McMaster who has done an outstanding job & will always remain my friend. There will be an official contact handover on 4/9.

McMaster, whose February 2017 appointment was lauded by politicians of both parties as well as many military officials, will be replaced by former UN ambassador John Bolton.

Known for his ardently hawkish military views, Bolton has not received the same warm welcome in establishment political and military circles.

McMaster's was the second resignation of the day among key players in Trump's orbit. Earlier on Thursday, Trump's lead lawyer in the special counsel's Russia probe, John Dowd, also announced his resignation.

CNBC's Eamon Javers contributed to this report.