"Unity makes the impossible, possible. Division makes the possible, impossible," Priebus told his party leadership in the RNC Spring Meeting address yesterday.
The same principle applies to the Republican Party, he said, noting that while millions of Americans will not vote until November, "they are making decisions right now about who they will vote for down the line."
He told the committee members that if they hope to win the White House, they have to rally behind the nominee after the Cleveland convention in July.
Priebus promised that the nominating process at Cleveland convention would be "fair, democratic and transparent," and that the Republicans would not give the nomination to anyone who does not secure a majority of delegates.
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"The rules say you have to have 1,237 delegates to be the nominee. We aren't going to hand the nomination to anyone with a plurality, no matter how close they are to 1,237. You need a majority. Almost only counts in horseshoes and hand grenades," he said.
Currently Trump, the Republican presidential front runner, is leading the delegate count but is still far behind the 1237 number. The other two White House aspirants Ted Cruz, and John Kasich do not have any mathematical way to get to that figure before the convention in Cleveland.
"Regardless of when we get a nominee, the bottom line is Republicans will leave Cleveland united and ready to win in November. And there's one more thing that we need to do. We need to stop Hillary Clinton. The country can't afford a dishonest career flip-flopper who is chomping at the bit to rubber stamp more of the extreme Obama agenda," he said.
"We need to be prepared for how they are going to throw everything but the kitchen sink at our candidates because it's her only hope for victory. In conclusion, we know the stakes are higher than ever for this election," he said.
"If we don't win in 2016, future generations might never know the kind of freedom and prosperity that has marked our nation from its birth. That might sound dramatic. But it's true," Priebus added.