WASHINGTON (AP) — House Republicans are set to begin a special investigation of the deadly attack on the U.S. diplomatic outpost in Benghazi, Libya, raising the stakes in a political battle with the Obama administration as the midterm election season heats up.

Democrats are considering a boycott of the select committee, which is expected to be approved formally when the Republican-led House votes early Thursday evening. Democrats fear their presence will provide legitimacy to what they believe will be a partisan forum. But they don't want to lose the ability to counter GOP claims and provide cover for potential witnesses.

In an opinion piece Thursday in USA Today, the congressman Speaker John Boehner chose to head the probe signaled he'd re-examine the entirety of the Benghazi attack, including some questions long dismissed by Democrats and even some senior Republicans. The GOP-led House Armed Services Committee concluded months ago that the U.S. military couldn't have responded in time to save Ambassador Chris Stevens and three other Americans. But Republican Rep. Trey Gowdy of South Carolina asked: "Was our military response during the pendency of the siege sufficient?"

Republicans have made Benghazi a central plank of their strategy to wrest control of the Senate from Democrats in November's traditionally low-turnout midterm elections. Accusations of an administration cover-up still rev up the GOP's conservative base. The legislation crafted by Boehner demands only that the select committee must be re-established when a new Congress begins in January, and includes no explicit financial constraints.

Republicans say the White House, concerned primarily with protecting President Barack Obama in the final weeks of his re-election campaign, misled the nation by playing down intelligence suggesting Benghazi was a major, al-Qaida-linked terrorist attack. They accuse the administration of stonewalling congressional investigators, pointing specifically to emails written by U.S. officials in the days after the attack but only released last week.

The Obama administration says officials tried to provide the public with the best information available after the attack at a time when U.S. embassies, consulates and other facilities were facing angry demonstrations across the Muslim world over a YouTube video mocking Islam's Prophet Muhammad. It originally attributed Benghazi to a similar protest that extremists hijacked, but retracted that account amid severe criticism. It says Republicans are persisting with Benghazi questions in the hopes of generating a scandal to gain political support.

Stung by the partisan nature of other congressional investigations of Benghazi, particularly a House Oversight Committee probe led by Rep. Darrell Issa, R-Calif., Democrats have voiced wide-ranging concerns over the scope and composition of the select committee. But they are split on whether to participate in the new select committee or boycott it.

Boehner has brushed aside Minority Leader Nancy Pelosi's calls for an evenly split committee, opting instead to appoint seven Republicans and five Democrats. The Democrats also say they have no guarantees they'll gain equal access to documents, participate in the issuing of subpoenas and enjoy the same right to question witnesses.

Like House Democrats, the administration has yet to say whether it will cooperate with the select committee. On Wednesday, White House spokesman Josh Earnest pounced on congressional Republicans for seeking campaign money off the investigation, describing a fundraising email earlier in the day as a "pretty good indication of political motivation."

The National Republican Congressional Committee's pitch said the GOP was "moving fast" to hold Obama and former Secretary of State Hillary Rodham Clinton "accountable for their actions" on the night of the Benghazi attack. It vowed that "no one will get away" from the select committee and asked people to become a "Benghazi Watchdog" by donating money. Suggested contributions started at $25.

Boehner on Thursday refused to criticize the fundraising appeal. Asked three times about the effort, he told reporters, "Our focus is on getting the answers to those families who lost their loved ones. Period."