Donald Trump on Monday lambasted Democratic presidential nomination dropout Bernie Sanders for giving into Hillary Clinton's nomination on Monday, saying Sanders "made a deal with the devil."
"She's the devil. He made a deal with the devil," Trump said referring to the agreement between the Vermont senator and Clinton.
"They are talking about Bernie cause he made a bad deal. He should have not made a deal. He would have gone down as doing something really important," Trump said.
"Once he made that deal, and believe me he has buyer's remorse. You know this guy has buyer's remorse."
Trump was speaking about a symbolic show of party unity during the Democratic National Convention when Sanders told the chairwoman from the convention floor that Hillary Clinton should be selected as the party's nominee.
During a town hall event in Columbus, Ohio, the Republican nominee also told supporters he thought the November election might be "rigged".
In the past few days Trump has faced criticism following his controversial comments about the Gold Star parents of a Muslim soldier killed in Iraq. Trump's presidential campaign appealed to Capitol Hill for support as his attacks on Khizr Khan and Ghazala Khan, the parents of a decorated American soldier killed in Iraq, drew sharp rebukes from fellow party members.
Trump's criticism of the Khans, who took the stage at last week's Democratic convention, sparked growing concern and dismay from Republican lawmakers responding to the latest Trump outburst to blindside his party colleagues.
Republican Senator John McCain, a former prisoner of war and the most prominent veteran in Congress, along with the commander of the Veterans of Foreign Wars, joined the chorus of condemnation, reflecting the highly regarded place the military and its veterans hold with many in the United States.
Trump's dispute with the Khans has dominated the White House campaign in recent days and underlined the uneasy alliance between many leading Republicans and the party's freewheeling, unorthodox nominee for the November 8 election.
Rob Wasinger, a onetime congressional candidate who has been working for the Trump camp on congressional outreach, sent an email to senior Senate aides saying, "We want to get several member statements out today on this, and would really appreciate your help."
A similar appeal was made to Republicans in the House of Representatives, according to a senior aide.
The appeal did not generate any help for Trump. A senior Senate Republican aide, who asked not to be identified, said Republican senators were pleased with Senate Majority Leader Mitch McConnell's statement on Sunday calling Captain Khan "an American hero" and noting "a travel ban on all members of a religion is simply contrary to American values."
At the same time, the aide said the controversy would probably not cause Republican senators to withdraw their endorsements of Trump.
In a convention speech delivered with his wife at his side, Khizr Khan showcased his son's military service and criticised Trump's call for a temporary ban on Muslims from entering the United States, holding up a copy of the US Constitution and suggesting Trump read it.
Since then, Trump has complained he was "viciously" attacked by the couple and suggested Ghazala Khan might not have been "allowed" to speak, implying her silence reflected restrictions placed on women by some traditional Muslims.
McCain, the 2008 Republican presidential candidate and current chairman of the Senate Armed Services Committee, issued a lengthy statement sharply criticising Trump's comments.
"While our party has bestowed upon him the nomination, it is not accompanied by unfettered license to defame those who are the best among us," said McCain.
His counterpart on the House Armed Services Committee, Representative Mac Thornberry of Texas, echoed McCain, saying in a statement he was "dismayed at the attacks Khizr and Ghazala Khan have endured after they spoke about their son's service and sacrifice."
The head of the 1.7 million-member Veterans of Foreign Wars also said Trump's attack on the Khans went too far. Trump and Clinton spoke to the group's national convention last week.
Trump's off-the-cuff insults and controversial proposals such as the Muslim ban and a plan to keep illegal immigrants out by building a wall along the Mexican border, have made many in the party establishment reluctant backers of his White House bid.
On Sunday, Democratic rival Clinton said Trump had scapegoated the parents. In addition to Senate Majority Leader McConnell, House Speaker Paul Ryan issued a statement supporting the family.