President-elect Donald Trump teed off on Hillary Clinton’s campaign team early Sunday, following the announcement that it would participate in the vote recount efforts started by Jill Stein, the Green party’s presidential nominee.

Mr. Trump took to his favorite social media platform, Twitter, calling the efforts “sad” and declaring that “nothing will change” despite the time and money that will be spent.

Hillary Clinton conceded the election when she called me just prior to the victory speech and after the results were in. Nothing will change — Donald J. Trump (@realDonaldTrump) November 27, 2016

The president-elect also mentioned Clinton’s remarks during one presidential debate, when she called it “horrifying” that Mr. Trump was declining to say he would absolutely accept the general election results.

Hillary's debate answer on delay: "That is horrifying. That is not the way our democracy works. Been around for 240 years. We've had free -- — Donald J. Trump (@realDonaldTrump) November 27, 2016

and fair elections. We've accepted the outcomes when we may not have liked them, and that is what must be expected of anyone standing on a - — Donald J. Trump (@realDonaldTrump) November 27, 2016

during a general election. I, for one, am appalled that somebody that is the nominee of one of our two major parties would take that kind -- — Donald J. Trump (@realDonaldTrump) November 27, 2016

of position." Then, separately she stated, "He said something truly horrifying ... he refused to say that he would respect the results of -- — Donald J. Trump (@realDonaldTrump) November 27, 2016

this election. That is a direct threat to our democracy." She then said, "We have to accept the results and look to the future, Donald -- — Donald J. Trump (@realDonaldTrump) November 27, 2016

Trump is going to be our President. We owe him an open mind and the chance to lead." So much time and money will be spent - same result! Sad — Donald J. Trump (@realDonaldTrump) November 27, 2016

Later in the afternoon, Mr. Trump himself seemed to question the validity of the election results, alleging without any evidence that there were “millions of people who voted illegally.”

In addition to winning the Electoral College in a landslide, I won the popular vote if you deduct the millions of people who voted illegally — Donald J. Trump (@realDonaldTrump) November 27, 2016

It would have been much easier for me to win the so-called popular vote than the Electoral College in that I would only campaign in 3 or 4-- — Donald J. Trump (@realDonaldTrump) November 27, 2016

states instead of the 15 states that I visited. I would have won even more easily and convincingly (but smaller states are forgotten)! — Donald J. Trump (@realDonaldTrump) November 27, 2016

Kellyanne Conway, a top adviser to the president-elect, defended Mr. Trump following the Twitter messages.

“This is the president-elect’s position right now and I would say he’s been incredibly gracious and magnanimous to Secretary Clinton at a time when, for whatever reason, her folks are saying they will join in a recount to try to somehow undo the 70 plus electoral votes that he beat her by,” Conway told CNN Sunday. (According to CBS News’ tally, Clinton trails Mr. Trump by 58 electoral votes. Clinton currently leads Mr. Trump by over 2.2 million votes in the popular vote contest, according to the Cook Political Report.)

On the Wednesday after the election tallies came in, Clinton, in a concession speech, had urged her supporters to “accept” the results.

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“Donald Trump is going to be our president,” Clinton said at the time. “We owe him an open mind and the chance to lead.”

Reince Priebus, Mr. Trump’s appointed chief of staff, said on “Fox News Sunday” that Clinton’s team had “cut a deal” with the Trump campaign about conceding the race: Once the Associated Press called the race for one candidate, the other would call within 15 minutes to concede.

Priebus said that’s exactly what happened on election night, but the ex-Republican National Committee chair wondered whether the Clinton campaign’s latest decision to participate in the recount efforts violated that agreement.

Mr. Trump’s tweetstorm early Sunday was a continuation of the president-elect’s rampage Saturday on Stein’s “ridiculous” recount attempts, when he issued a lengthy statement about how the donations -- now amounting to over $6 million -- were just meant to “fill her coffers with money.”

“This is a scam by the Green Party for an election that has already been conceded, and the results of this election should be respected instead of being challenged and abused, which is exactly what Jill Stein is doing,” he said in a statement issued by his transition team.

On Saturday, Marc Elias, the Clinton campaign’s general counsel, announced that the campaign would “participate” in the Wisconsin recount, for which Stein’s representatives have already filed the paperwork. (If Stein follows through with petitioning for recounts in Pennsylvania and Michigan, the Clinton campaign also intends to join their efforts in those states.) In Wisconsin, Mr. Trump’s vote margin numbered just over 27,000 ballots. If the three states were to flip to Clinton victories, she would win the general election with 278 electoral votes, though that scenario seems very unlikely. It is rare that recounts change the result of a race.

Wisconsin’s elections commission is slated to discuss the state’s recount timeline early Monday morning on a conference call with reporters.

The state will be working to complete the recount by the Dec. 13 federal deadline.