Colorado Springs, Colorado (CNN) Sen. John Cornyn said Sunday he'd worked the phones all weekend trying to win support for the Senate health care bill and was "optimistic" the legislation would pass.

"It's hard," he told a small group of reporters when asked how negotiations were going between sessions at the Koch retreat. "But there's no excuse for failure. ... When people want to get to 'yes' you can have good faith negotiation and get them there."

"But it's going to be close," Cornyn said. He noted that he had been working directly with Republican Sens. Ted Cruz of Texas, Mike Lee of Utah, Ron Johnson of Wisconsin, Rand Paul of Kentucky and Dean Heller of Nevada to address their differing concerns about the bill.

Senate Majority Whip John Cornyn

When asked whether the Senate could wait until after the Fourth of July recess, he suggested that would weaken the bill's chances.

"We don't have the luxury of waiting around," he said. "It's not going to get any easier." The Texas senator described the period around August 1 as the "drop-deadline."

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