He may be gathering support among top Republicans on and off Capitol Hill, but several influential Evangelical leaders are holding off on backing presumptive Republican presidential nominee Donald Trump until Trump names a running mate.

According to POLITICO, Iowan social conservative leader Bob Vander Plaats, Concerned Women for America’s Penny Nance and others haven’t decided to oppose Trump, but nor are they jumping on board his candidacy. One key factor in their decision will be whether he selects a conservative running mate who, to quote POLITICO, will “compensate for Trump’s many heresies.”

Tony Perkins of the Family Research Council explained that negative comments Trump has made about women will be leveraged against him in the general election. “That is going to be used to suppress evangelical support and turnout for him,” said Perkins. “He has to counter that. The only way he counters that is … [with a] running mate, how he vets judicial nominees and what does he do with the party platform.”

It remains to be seen whether Trump will actually garner the grassroots influence and support of the evangelical leaders still on the fence, although the leaders still believe their endorsements and networking matter.

“There’s a big difference between me saying I don’t think we should do a third party, and giving a full-throated endorsement in which I actually work for him and get out the vote for him,” said Nance, adding that she’s not at all committed yet to getting her grassroots backers to do the latter. “It remains to be seen how involved our ladies will be.

“Door-to-door leaflets, sign waving, that’s the thing my ladies do,” she continued. “We’re the legit activists. We do it for free. Phone banking, hours and hours of phone banking, that’s a necessary part of the campaign. You can’t buy that.”

The vocal opposition by the evangelical and Republican leaders comes on the heels of Trump’s spat with Dr. Russell Moore of the Ethics and Religious Liberty Commission of the Southern Baptist Convention. After Moore criticized Trump on CBS’ Face the Nation on Sunday, Trump tweeted that that Moore was “…truly a terrible representative of Evangelicals and all of the good they stand for. A nasty guy with no heart!”

Moore responded by tweeting 1 Kings 18:17-19, a Bible verse where the prophet Elijah confronted King Ahab about abandoning the Lord’s commands and followed false gods. Trump has not responded to Moore’s tweet.

The concerns of the groups cited by POLITICO are similar to those of many social conservatives who see Trump as inconsistent on their issues. He has changed positions several times on the morality of abortion and funding Planned Parenthood, and has said his view on the issue of same-sex “marriage” is evolving even as he claims to oppose it. His statement that he is a Christian who has never asked forgiveness from God, other Biblical faux pas and bragging about his sexual prowess also have not endeared him to the powerful conservative constituency.

Not all religious leaders have joined Nance and Perkins. Liberty University president Jerry Falwell, Jr. endorsed Trump early on, and Dr. Robert Jeffress, pastor of First Baptist Church in Dallas, has provided unqualified support for the billionaire businessman.

Trump faces mixed support from influential GOP players and those who hold the tenets of social conservatism in high regard. Republican House Speaker Paul Ryan has said that he is not sure if he will back Trump, although they have a scheduled meeting on Thursday. Many senators are backing Trump, with notable exceptions like Mike Lee of Utah refraining from an opinion and Nebraska’s Ben Sasse declaring his outright opposition.

Former primary opponents have been mixed, with Senator Lindsey Graham and former Florida governor Jeb Bush saying they will not back Trump. However, former governors Rick Perry and Bobby Jindal, along with Mike Huckabee, have stood behind the expected nominee.

Many key GOP donors want nothing to do with Trump, according to POLITICO. For example, the Koch brothers have reportedly claimed they may sit out the Republican campaign, and other major GOP donors are weighing their options. George Seay, a Dallas investor and major fundraiser for former candidate Marco Rubio, says he’s at a stalemate on contributions for Trump. “I have gotten involved in some Senate races,” he says, “but I’m pretty much sidelined politically for now.”

For now, a significant number of evangelical leaders, major GOP players and top donors appear to be waiting to see how things progress, who Trump selects as a running mate and whether he maintains consistently conservative positions or continues to change on key issues.