Sen. Bernie Sanders’ effort to persuade Democratic superdelegates to switch to his side from Hillary Clinton’s so far is more a rhetorical flourish than an active campaign.

As Clinton has widened her lead over Sanders in pledged delegates won in primaries and caucuses over the past month, the Vermont senator has turned to making a case to the more than 700 party officials and office holders who are unbound delegates to the national convention. His argument: he’s “entitled” to the superdelegates from states he’s won and he’d be the stronger candidate to face off against Donald Trump in the general election.

While that’s helped buoy Sanders’ supporters and donors, it hasn’t done much to chip away at Clinton’s overwhelming lead in the nominating race.

Tad Devine, Sanders’ senior adviser, said the campaign is making an effort to sway the superdelegates who haven’t yet publicly committed to either Sanders or Clinton. But that universe, an estimated 152 superdelegates, would make only a small dent in Clinton’s lead. Devine said they won’t start “aggressive outreach” to Clinton backers until after the last primary in June.

“We’re not going to spend a lot of time talking to people who’ve made a public endorsement until we feel we’ve got to the best possible moment to make that kind of appeal, and to us that’s going to come after the voting,” he said.

The effort is constrained by time and the numbers. Clinton has 2,205 delegates, including 522 superdelegates, according to a tally by the Associated Press. That’s 178 short of the 2,383 needed to win the Democratic nomination. Sanders’ delegate count stands at 1,401, and just 39 of those are superdelegates.

The Sanders campaign has a team of staffers keeping track of calls to superdelegates and where they stand, according to a Sanders aide who works on political outreach. Over the course of the race, the campaign has reached out at some point to every superdelegate either in person, over the phone, by e-mail or in a weekly newsletter, said the aide, who wasn’t authorized to speak publicly about internal operations.

But the effort has yielded modest results, and Clinton has won the majority of the superdelegates in nearly every state Sanders has won.

The Sanders campaign has disavowed and discouraged volunteers from contacting superdelegates, but as Sanders has talked more about superdelegates, some have noticed increased outreach on social media and via e-mail.

Marge Hoffa, the vice chairwoman of the Minnesota DFL Party, said she hadn’t been in touch with the campaign, but had heard from Sanders supporters. She said that in recent weeks, the intensity of that outreach has increased. “I just want this to go away,” Hoffa said.

Hoffa said her main reason for supporting the front-runner is her lead in pledged delegates.

“That is what I said from the beginning,” Hoffa said. “I said I will support her, but if Bernie Sanders ends up with more pledged delegates I will give him my support at the convention because I’m not going to change what the majority of people out there want.”