For Ms. Gillibrand, Ross Offinger, a former fund-raiser for the New York senator, has quietly been reaching out to donors to feel out interest in a pro-Gillibrand super PAC, floating the name of Bill Hyers, who ran Ms. Gillibrand’s first campaign for the House in 2006 and served as Martin O’Malley’s campaign manager in 2016, according to a person familiar with the calls.
“We would discourage any activity of this type at this point,” Mr. Caplin said.
In some cases, strategists have floated the idea of delaying the creation of super PACs until deeper in the race to minimize blowback; of course, that risks donors deciding not to cut checks later.
In Texas, Mr. O’Rourke broadly denounced super PACs throughout his Senate bid, but some still got involved late to attack his Republican opponent. The outside spending did not seem to smudge the reputation of Mr. O’Rourke, who raised record sums online.
In 2012, Ms. Warren struck a deal with her Republican opponent to denounce super PACs and give away money to charity if they got involved. People close to her said that she is unlikely to seek super PAC assistance in 2020 and that she is unlikely to endorse any candidate who would if she does not run.
In Ohio, there is already a “Draft Sherrod Brown” effort in the works for the Democratic senator, organized by his former finance chairman, Michael Wager, and Nan Whaley, the mayor of Dayton. Mr. Wager said the effort could eventually become a pro-Brown super PAC.
Almost every would-be campaign has been quietly gauging donors on their level of commitment.
Guy Saperstein, a Democratic donor in California who publicly pledged $1 million for a pro-Warren super PAC in 2016 if she challenged Mrs. Clinton, said he had attended two recent dinners with Ms. Warren and he “had some feelers from some people associated with her” about if he would support her if she ran this time. (Mr. Saperstein said he had “begged” advisers to Mr. Sanders to set up a super PAC in 2016. They refused.)
Like so many donors, Mr. Saperstein is not ready to commit in 2020 — yet.
“I’ll probably give to Bernie and Elizabeth to start out the primaries,” he said. “Then I’ll sit back and wait to see how things develop.”