Republican presidential candidate businessman Donald Trump speaks as he stands among six rivals for the presidential nomination during the Fox Business Network Republican candidates debate in Charleston, South Carolina, Jan. 14, 2016. Reuters/Randall Hill

While the exact percentage points vary, Donald Trump maintains a firm lead in the polls ahead of the Thursday night Republican presidential debate in Des Moines, Iowa, which the celebrity businessman has decided to sit out. With less than a week before the Iowa caucus, candidates have one last shot to persuade the pool of undecided voters.

Here's a look at the Republican presidential candidates with the field's highest levels of support among potential voters ahead of Thursday night's debate.

Donald Trump

Republican presidential candidate Donald Trump answers questions from reporters after being endorsed by Maricopa County Sheriff Joe Arpaio (left) before a campaign rally in Marshalltown, Iowa, Jan. 26, 2016. Reuters/Brian Snyder

The author of “How to Get Rich” leads the still crowded pack of Republican candidates, with 41 percent support in the latest CNN/ORC poll released Tuesday. The poll surveyed 405 adults between Jan. 21-24, 2016, with a sampling error of 5 percent. Four percent of voters said they still had no opinion about the candidates, while 3 percent said they were interested in a candidate not listed in the survey.

In a Washington Post/ABC News poll conducted from Jan. 21-24, 2016, with 1,001 adults surveyed and a margin of error of 3.5 percentage points, Trump led the pack with 36 percent support.

Sen. Ted Cruz

Republican presidential candidate Ted Cruz greets attendees at a campaign event in Osceola, Iowa, Jan. 26, 2016. Reuters/Jim Young

The Texas senator came in second place in the polls, with 19 percent support in the CNN/ORC poll and 20 percent in the Washington Post/ABC News. Cruz picked up the endorsement of Iowan evangelical and president of the Christian conservative group Family Leader, Bob Vander Plaats, this week, much to the disappointment of Trump, who had been trying to woo him.

Sen. Marco Rubio

Republican presidential candidate Sen. Marco Rubio arrives for a town hall at the Sheraton Hotel in West Des Moines, Iowa, Jan. 26, 2016. Reuters/Aaron P. Bernstein

When it comes to third place, Rubio falls far behind Cruz with 8 percent support in both the CNN/ORC and Washington Post/ABC News polls. Rubio was endorsed by the Des Moines Register in an editorial that described him as “the party’s best hope.”

Ben Carson

Ben Carson
Republican presidential candidate Ben Carson speaks at a Trust in God town hall at Simpson College in Indianola, Iowa, Jan. 25, 2016. Reuters/Scott Morgan

Once a front-runner, the retired neurosurgeon has slipped in the polls, coming in fourth place with only 6 percent support in both the CNN/ORC and Washington Post/ABC News polls.

Former Florida Gov. Jeb Bush

Republican presidential candidate Jeb Bush smiles as he holds a gun presented to him at Sturm, Ruger & Co. in Newport, New Hampshire, Jan. 21, 2016. Reuters/Mary Schwalm

Toward the bottom of the pack, Bush only has the support of 5 percent of voters surveyed in both polls. Bush is closely trailed by New Jersey Gov. Chris Christie with 4 percent support and former Arkansas Gov. Mike Huckabee and former Kentucky Sen. Rand Paul, both with 3 percent support.