It is another instance of Republicans coming out against the party's presidential nominee. In recent weeks, a number of high-profile Republicans have said they cannot support Trump's candidacy.
"We believe that Donald Trump’s divisiveness, recklessness, incompetence, and record-breaking unpopularity risk turning this election into a Democratic landslide, and only the immediate shift of all available RNC resources to vulnerable Senate and House races will prevent the GOP from drowning with a Trump-emblazoned anchor around its neck," the letter reads.
It said Trump's chances of becoming president are "evaporating by the day," in large part because of feuds and inflammatory comments that are alienating voters. The letter said they include his spat with the parents of a Muslim Army captain who was killed in Iraq, calling on Russia to find Democratic nominee Hillary Clinton's missing emails, showing a "total ignorance" of foreign policy and "deliberately and repeatedly lying about scores of issues, large and small."
The RNC and Trump's campaign did not immediately respond to a request for comment.
The letter cites a number of polls that show Trump losing ground to Clinton nationally. It also points out his animosity toward other Republicans, including his claims that Sen. Ted Cruz's father may have been linked to President John F. Kennedy's assassin, stating he would start a super PAC that could be used to fight other Republicans, calling Sen. Mark Kirk (R-Ill.) a loser in front of his Senate colleagues and initially refusing to support House Speaker Paul Ryan's primary campaign.
Andrew Weinstein, a former spokesman for Bob Dole and Newt Gingrich, said the letter was a cooperative effort among Republicans who were growing increasingly concerned at the idea that Trump could imperil the Republican majority in Congress. He said at least 17 former RNC staffers have signed the letter, which will be delivered to the committee next week. Signatures are still being collected.
Weinstein said the signatories aren't endorsing a particular candidate and vary on whom they will support in November. Weinstein has said he plans to vote for Clinton.
"To me, what that shows is this is almost like a family intervention, where they are trying to rescue a family member who is engaged in self-destructive behavior, which is what the RNC is doing right now," he said.
Weinstein is a veteran of Dole's 1996 campaign. Weeks before Election Day in 1996, as it became clear that Dole would not win the election, Republicans started to urge congressional candidates to make the argument: "Let's not give Clinton a blank check." In late October of that year, the National Republican Congressional Committee spent $4 million on television ads in contested congressional districts. Republicans lost nine seats but managed to hold the House. Weinstein said the letter signers want this effort to start much earlier.
"It's not a matter of electing Donald Trump," Weinstein said. "It’s a matter of saving Congress."
This post has been corrected. Bruce Bartlett was not a member of President George W. Bush's cabinet and Gordon Humphrey was not a congressman.