WASHINGTON — In ways both subtle and blunt, Hillary Rodham Clinton’s campaign is sending a message to Vice President Joe Biden about his potential presidential campaign: This won’t be easy.

As Biden ponders a challenge to Clinton for the Democratic nomination, she has rolled out a string of high-profile endorsements in the early-voting contests of Iowa and South Carolina and scheduled an onslaught of fundraisers across the country in the effort to throw cold water on a possible Biden bid.

Donors who have publicly expressed support for a Biden run have been contacted by the Clinton team, according to donors and Democratic strategists who spoke on condition of anonymity because they were not authorized to discuss the private conversations. Even Clinton herself has made a few calls, they said, to express her disappointment.

While Clinton and her team speak warmly of Biden in public, they have taken steps to show their dominance over the party’s establishment and President Barack Obama’s political infrastructure in hopes of quietly discouraging the vice president from entering the race.

The effort comes as Clinton and the Democratic field of candidates prepare to address members of the Democratic National Committee on Friday during their summer meeting in Minneapolis. The night before her formal address, Clinton made her case in private briefings to attendees. Meanwhile, representatives from a super PAC backing Biden plan to woo delegates in his absence.