Donald Trump and Hillary Clinton’s truce and efforts to “come together” after their bitter White House race appeared to fray this weekend when Clinton joined in a vote recount effort that the President-elect assailed in a series of Tweets Sunday.

In the posts, Trump claimed that "millions" of people cast illegal votes in this month's presidential election, and claimed that the press was covering the matter unfairly.

Trump further contended that if the popular vote determined the presidency, "It would have been much easier for me to win" it because he would have altered his campaign to pile up overall vote totals, not Electoral College votes.

The real estate mogul also tweeted part of Clinton's concession speech, when she told supporters they must accept that "Donald Trump is going to be our president," and snippets from her debate remarks, when she denounced the Republican nominee for refusing to say in advance that he would accept the Election Day verdict.

There's been no indication of widespread vote manipulation, illegal voting or hacking that materially affected the outcome one way or the other. It's that very lack of evidence that suggests Trump is likely to prevail in recounts.

Trump's social media storm came one day after a Hillary for America lawyer said that Clinton would join in a vote-recall effort by Green Party Candidate Jill Stein.

The attorney, Marc Elias, said Clinton was taking the step “to ensure the process proceeds in a manner that is fair to all sides."

Stein has already raised at least $5.4 million in her effort to recount votes in Michigan, Pennsylvania and Wisconsin -- states that were the key to Trump's upset victory. She began the process Friday by officially requesting a review in Wisconsin.

Stein has argued the recount is intended to test the integrity of the U.S. voting system, amid so-far unfounded speculation that Russia tampered with the process.

However, the effort also could undo the 70-plus electoral votes by which Trump beat Clinton.

Trump won Wisconsin and Pennsylvania and, as of Wednesday, held a lead of almost 11,000 votes in Michigan, with the results awaiting state certification Monday.

Stein received only about 1 percent of the national vote, which has prompted Trump to call her effort a fundraising “scam.”

“I would say (Trump) has 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,” senior Trump transition team adviser Kellyanne Conway said on CNN’s “State of the Union.”

“She congratulated him and conceded to him on election night. … The idea that we are going to drag this out now where the president-elect has been incredibly magnanimous to the Clintons and to the Obamas is incredible.”

Meanwhile, Conway refused to rule out the possibility of further investigating Clinton over her use of a private email server while secretary of state between 2009 and 2013.

Conway made clear that Trump said only that he wouldn’t rule out another possible email probe because new evidence could emerge and he wouldn’t want to undercut the authority of federal and congressional investigators.

The FBI this summer concluded its one-year investigation into Clinton using the private server by saying she was “extremely careless” and that some of the emails included classified information.

However, the investigation was effectively closed without criminal charges being recommended to the Justice Department.

Trump, in his presidential debates with Clinton, also suggested that if elected he would appoint a special prosecutor for the matter.

Trump planned to return to New York on Sunday after spending Thanksgiving weekend at his West Palm Beach estate. His transition team said the president-elect had scheduled a series of meetings Monday with prospective administration hires.

The Associated Press contributed to this report.