Does President Trump prefer iPhone or Android?

Trump's social media director, Dan Scavino, said late Tuesday on Twitter that the president has been tweeting from "his new iPhone" for the past couple of weeks. But a tweet bearing the hallmarks of Trump's combative style came from an Android device as recently as Saturday.

The matter has potential national security implications.

During the early weeks of his presidency, Trump came under scrutiny over reports he was continuing to use his old, unsecured Android phone to send tweets to the 27 million followers of his @realDonaldTrump account.

"The national security risks of compromising a smartphone used by a senior government official, such as the President of the United States, are considerable," two Democratic senators wrote in a letter to Defense Secretary James Mattis last month asking for more information about the president's mobile devices.

.@POTUS @realDonaldTrump has been using his new iPhone📱for the past couple of weeks here on Twitter. Yes, it is #POTUS45 reading & tweeting! — Dan Scavino Jr. (@DanScavino) March 29, 2017

At the time of his inauguration, Trump was reported to have traded in his Android phone, believed to be a Samsung, for a secure device. But @realDonaldTrump tweets marked as coming from "Twitter for Android" kept appearing.

The concern, according to the senators, is that hackers may be able to break into an unsecured device and "turn on audio recording and camera features, as well as engaging surveillance tools that allow location and other information tracking features."

Related: Senate Democrats want answers about Trump's phone

Earlier this month, the Android-marked tweets dried up for a while and more iPhone tweets appeared. Some news organizations suggested the president might have switched phones.

But on Saturday, a typical Trump tweet with the Android tag popped up, declaring that "ObamaCare will explode."

The White House declined to say whether any of the devices being used by Trump were secure.

"We don't discuss the security measures that are or have taken place," press secretary Sean Spicer told CNNMoney by email Wednesday.

Related: The Presidential Records Act and @realdonaldtrump

Intelligence officials went to great lengths to provide former President Barack Obama with a secure BlackBerry that he could use to communicate with his advisers.

Security researchers say it's tougher to compromise iPhones than Android devices, but not impossible.

Trump used an iPhone early in his campaign, a time when he also criticized Apple (AAPL) for making products overseas. In February 2016, he called for a boycott of Apple products over the tech giant's refusal to help the FBI break into an iPhone used by one of the San Bernardino attackers.

"I use both iPhone & Samsung. If Apple doesn't give info to authorities on the terrorists I'll only be using Samsung until they give info," he tweeted. Apple didn't back down, and Trump eventually appeared to stop tweeting from an iPhone.

Related: Trump voters to president: Stop Twitter rants

Some observers had used Trump's iPhone abstinence as a way of guessing which tweets from the @realdonaldtrump account he'd actually written himself.

Android-marked tweets, believed to be direct from Trump, tended to be angrier and use all caps liberally. More restrained tweets, often promoting Trump events, would be posted from an iPhone, presumably by aides.

Now, both styles of tweet are coming from iPhones, with a little Android still mixed in.