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Inside Republicans' failed attempts at blocking Donald Trump's rise

Donald Trump, seen in reflection, poses for a portrait following an interview with The Associated Press at the Trump National Golf Club in Sterling, Virginia, Dec. 2, 2015.

Andrew Harnik/AP

In a time before establishment party figures like New Jersey Gov. Chris Christie rallied behind Donald Trump with their endorsement -- a time before Trump crushed his rivals in three of the four early nominating contests -- some Republican operatives were coalescing around the idea that the current GOP front-runner could actually be stopped.

Last fall, Republican strategists Alex Castellano and Gail Gitcho -- both old hands at presidential campaigns -- asked several donors about creating a super PAC dedicated to halting Trump's momentum. They reached out to several big name Republican financiers, including casino mogul Sheldon Adelson and hedge fund manager Paul Singer, about their proposed "ProtectUS" super PAC.

In a memo distributed to donors and party leaders, the two laid out an executive summary of their plan, labeling their mission as "the last chance to rescue America."

"Donald Trump could be the GOP nominee," they warned in the memo, obtained by CBS News and first reported by the New York Times. "If Trump wins the Republican nomination, it's assured that we lose the White House ... If Trump wins, everyone loses: We not only lose the White House in 2016, but we also lose the Senate, competitive gubernatorial elections and moderate House Republicans."

Their hope was to push voters into imagining "Donald Trump in the Big Chair in the Oval Office, with responsibilities for worldwide confrontation at his fingertips."

"Only then, we believe, will Republicans see the danger and risk of a Trump Presidency," they wrote. "Once these doubts are raised, Trump's business record of bankruptcies, as well as his support of Canadian-style health care and other positions he shares with Hillary Clinton, can begin to pry GOP voters away."

But their plans never came to fruition.

After the effort failed to pick up steam among the GOP's donor base, the super PAC idea was abandoned -- and, as one Republican strategist told CBS News, it's "too late now."

Since last year, other party leaders have attempted to stymie Trump's rise.

A Times report published Saturday detailed further efforts to veer the Trump train off the tracks, including pushes to unite Republicans behind just one presidential rival, like Florida Sen. Marco Rubio. Even the 2012 GOP presidential nominee, Mitt Romney, has tried to use his influence in the primary race, urging Ohio Gov. John Kasich to drop out. But heading into the Super Tuesday nominating contests, the field still remains split.

Another attempt took place at a Republican governors meeting last week, where Maine Gov. Paul LePage called for his fellow state heads to pen an open letter "to the people" against Trump.

LePage's colleagues, according to the newspaper, never took up the suggestion.

Six days later, LePage gave his endorsement to Trump, on the heels of Christie's own nod to the New York businessman.

CBS News' Julianna Goldman contributed to this report.