Republican Sean Parnell, who last week suspended his candidacy for Pennsylvania’s open Senate seat after he lost a fight over custody of his three children, has left a gap in the race and led to speculation of who will fill it, reports the Philadelphia Inquirer.

Parnell’s withdrawal comes as many in the state Republican Party remain undecided about their field and represents a major blow to former President Donald Trump, who had enthusiastically endorsed Parnell in September with the encouragement of his eldest son.

Other potential candidates include conservative commentator Kathy Barnette, real estate investor Jeff Bartos and Carla Sands, Trump’s ambassador to Denmark.

Also swirling is a suggestion from Mehmet Oz — the cardiac surgeon and longtime host of TV’s “Dr. Oz Show” who gained fame as a protege of Oprah Winfrey — that he is being encouraged to enter the Republican primary.

Hedge fund manager David McCormick is another potential candidate. He is expected to visit with some top GOP insiders next week and has been calling political leaders and donors throughout the state. U.S. Rep. Keith Rothfus, a Western Pennsylvania Republican, is also exploring a bid.

Trump spokesperson Taylor Budowich said Trump and Parnell spoke before Parnell’s announcement and that Parnell informed Trump of his intention to suspend his campaign, given the decision.

He said on Twitter that the Pennsylvania Senate race “remains a top priority” for the former president and that “rallying our movement behind the best America 1st candidate remains critical.”