Updated

Republican Party heavyweights are flocking to Kansas in a bid to boost longtime GOP Sen. Pat Roberts, in the latest sign that a recent and bizarre shakeup in the race has put his seat in toss-up territory.

Arizona Sen. John McCain was stumping for Roberts on Wednesday, in the hopes of gaining some traction with Kansas’ more center-right constituents. McCain is slated to make another appearance for Roberts in Topeka on Thursday.

On Monday, Bob Dole, the former presidential candidate who represented Kansas for decades in the Senate, delivered a nearly hour-long speech in support of Roberts’ re-election in Dodge City.

"Pat and I have been friends for some time," Dole said. "When I had a problem in the House getting a bill passed, I'd call Pat."

Former Florida Gov. Jeb Bush also is scheduled to appear in Wichita next week for a grassroots rally and fundraiser.

The sudden national attention on the race is a sharp turnaround for Roberts, who has served in the Senate virtually unopposed for nearly two decades.

The tides turned for the 78-year-old former Marine after Democratic nominee Chad Taylor’s abrupt decision to drop out of the race. That decision – while sparking widespread speculation over the political motivations at play -- immediately turned the election into a much tighter contest between Roberts and independent political newcomer Greg Orman.

When Orman and Taylor were in the race together, polls showed Roberts leading by a healthy margin. But with Taylor out, polls show Roberts potentially in trouble. A Fox News poll released last week showed Orman leading Roberts 48-42 percent in a head-to-head race. Since that poll, Kansas’ Supreme Court ordered Taylor’s name off the ballot, effectively creating such a contest.

Orman, a former businessman with an estimated wealth between $21.5 and $86 million, made his first, albeit brief, attempt at politics in 2008 as a Democratic candidate in Kansas’ Senate election against Roberts, but dropped out of the race before the primary.

Roberts campaign adviser Chris LaCivita has said that Orman is “nothing more than a liberal masquerading as an independent,” and that they are confident that Roberts’ track record with conservative voters will be enough to pull him through the race.

Political oddsmakers still are reassessing the contest and generally gauge it as competitive – complicating Republicans’ hopes of gaining a net six Senate seats to regain control of the chamber.

A Tuesday report on FiveThirtyEight.com estimates Orman has a 61 percent chance of unseating the three-term senator, but indicates the race is still too close to call.

Aside from Dole, McCain and Bush, Sen. Rand Paul, R-Ky., and Rep. Paul Ryan, R-Wis., reportedly are scheduled to make appearances for the senior senator in October.

In addition to bringing out the heavyweights of the party to raise Roberts’ credibility, the GOP is using Orman’s history as a businessman to damage his, including highlighting ties that Orman has with ousted Goldman Sachs board member, Rajat Gupta, who currently is serving a two-year term in federal prison for insider trading.

The Hill quoted an aide for Orman saying that despite any ties to the convicted felon, Orman is still in the position to carry the race and the people of Kansas are tired of what he calls the “Washington dysfunction,” and they are “tired of Pat Roberts.’’

Republicans have held both Senate seats in Kansas -- a famously red state -- for the last 76 years.

Alana Wise and The Associated Press contributed to this report.