Former White House national security adviser John Bolton returned to Twitter on Friday with a series of cryptic posts and a claim that the White House refused to grant him access to his personal Twitter account.

Why it matters: House Democrats have sought his testimony in the ongoing impeachment inquiry because he is considered a key witness in the Ukraine investigation. While there's online speculation his tweets could be tied to that, it's also worth noting that he has a forthcoming book about his time in the Trump White House.

The big picture: Bolton has been on a two-month Twitter hiatus since he resigned from the Trump administration earlier this year. He tweeted Saturday, touting support for House and Senate candidates in 2020 through his political action committee.

What he's saying:

"Glad to be back on Twitter after more than two months. For the backstory, stay tuned........"

"We have now liberated the Twitter account, previously suppressed unfairly in the aftermath of my resignation as National Security Advisor. More to come....."

"Re: speaking up -- since resigning as National Security Advisor, the @WhiteHouse refused to return access to my personal Twitter account. Out of fear of what I may say? To those who speculated I went into hiding, I’m sorry to disappoint!"

"In full disclosure, the @WhiteHouse never returned access to my Twitter account. Thank you to @twitter for standing by their community standards and rightfully returning control of my account."

On Saturday he wrote:

"Let's get back to discussing critical national-security issues confronting America. The threats are grave and growing. The presidency and control of the House and the Senate will all be decided in less than one year. It's time to speak up again! #JohnBolton"

"Many are speculating about what I plan to do next. I’m excited to tell you what I’ve been working on. "

— John Bolton tweeted, linking to his PAC

Go deeper: Bolton's chaotic White House departure