President Bush is slated to headline a September fund-raiser for Senate Republicans in what could be the GOP's last big push for large corporate contributions before a ban on them takes effect after the election.

In a letter urging potential donors to attend, Vice President Dick Cheney says it is uncertain whether Republicans will regain their Senate majority in the fall election.

"I can't overstate the challenge we face," Cheney wrote in the Aug. 9 letter. "The party of our president hasn't taken control of the Senate from an opposing party at the midterm since direct senatorial elections began in 1914."

The fund-raising packet offers tickets to the Sept. 25 dinner for $2,500, along with memberships to the Republican Senatorial "Inner Circle" donor group for $2,000 a year.

Bush helped raise record totals of at least $30 million at the Republican National Committee's gala and the House-Senate GOP presidential dinner in Washington last spring. He has also aggressively hit the fund-raising trail for Republican candidates around the country, raising roughly $105 million in all for the GOP so far this year.

Bush's fund-raising has gotten a boost from large corporate contributions known as "soft money," unlimited donations that a new campaign finance law will bar the national political parties and congressional candidates from collecting after the November election.

The September dinner at the Mayflower Hotel for the National Republican Senatorial Committee includes a day of meetings with key lawmakers for Inner Circle members.

Among those, donors can attend an "Inner Circle Challenger Lunch/Photo Op" with congressmen trying to unseat Democrats in key Senate races, including Rep. Lindsey Graham of South Carolina, Rep. John Thune of South Dakota, Georgia Rep. Saxby Chambliss and Iowa's Greg Ganske.