CLEVELAND (AP) — It's the first really good news — and really bad news — for Republicans seeking the presidential nomination: Who's in Thursday's first prime-time debate and who's not.

Among the ten top-polling Republican presidential hopefuls selected to participate in the event, all eyes will probably be on outspoken billionaire businessman Donald Trump, joined by former Florida Gov. Jeb Bush, Wisconsin Gov. Scott Walker and other contenders.

Seven others will be excluded, including former technology executive Carly Fiorina and former Texas Gov. Rick Perry, relegated to a pre-debate forum and second-tier status in the party's crowded field. Fox News, the host of the debate, announced Tuesday the 10 Republican White House hopefuls who will take part.

Trump, after launching his campaign with a speech that labeled Mexican immigrants as "criminals" and "rapists," was initially thought to have no chance in the race, but the latest polls show him far outdistancing the top-tier mainstream Republican candidates. However, his negative numbers in the polls are also high and most observers remain skeptical about his chances of securing the nomination.

Some Republicans fear that Trump's rhetoric on immigration and other issues could hurt the party.

"I probably am the target," he said Wednesday on ABC's "Good Morning America." He said he did not want to attack any of his rivals and preferred to "just discuss the issues" in the course of a "very civil" debate. Still, he made clear that if attacked, he would have "to do something back."

The debate will be a key test for Trump. Some polls show his backing has grown to nearly double that of Bush, the brother and son of two former U.S. presidents.

The announcement comes after the Republican Party worked aggressively to improve its debates ahead of the election season. Yet with the largest field of contenders in modern memory, organizers say something had to give to ensure the debate in Cleveland didn't turn into a nationally televised circus.

"We never ever envisioned we'd have 17 major candidates," said Steve Duprey, New Hampshire's representative to the Republican National Committee who helped craft the debate plan. "There's no perfect solution."

Republican officials worked closely with TV executives, although the networks have the final say about which candidates will be allowed on stage for their televised events.

Fox News will be hosting the event, the first of six party-sanctioned debates before primary voting begins in February. The network says it used a selection of national polls to make this week's cut.

Many candidates are grouped together in the single digits, most separated by a number smaller than the margin of error.

Republican officials were particularly concerned about Fiorina's status, hoping she would help balance Democratic presidential hopeful Hillary Rodham Clinton's push to rally women to her candidacy. Trump's recent surge in the polls was particularly damaging to Fiorina.

Candidates already began to turn their attention toward Trump.

Asked about Trump while courting religious conservatives on Tuesday, Bush said the businessman's rhetoric on immigrants is "wrong." ''We have a different tone and a different view," he said.

"I respect the fact that he's the front-runner for the Republican nomination," Bush continued. "This is a serious thing. But I think to win and govern the right way — we have to unite rather than divide."