A one-time Republican Kansas House speaker and two other retired GOP lawmakers Monday endorsed the candidacy of Democrat Paul Davis for governor.

Davis, the House minority leader from Lawrence, is seeking the Democratic Party's nomination and is the presumed central rival to Republican Gov. Sam Brownback in the November general election.

The endorsements are part of a push by the Davis campaign to present a bipartisan argument against a second term for Brownback, who easily won election in 2010 following a career in the U.S. Senate and U.S. House. The Brownback campaign responded by pointing to the governor's education, environmental and pension reforms welcomed by Republicans and Democrats.

Wendell Lady, who represented Overland Park for 14 years and ran for governor in 1982, said his perspective was influenced by Brownback's imposition of supply-side economic tax policy made visible by elimination of business income tax for thousands of companies and by a pledge to reduce individual income tax rate to zero.

"His income tax plan is the most unfair tax legislation ever enacted in Kansas," Lady said. "Not only does it threaten to bankrupt the treasury, but it will devastate the quality of education that the state is able to provide at all levels."

James Echols, chair of Democrats for Brownback, said members of both major political parties in Kansas appreciated the governor's leadership during an economically challenging time.

"Sam Brownback has shown the right mix of courage and vision to lead our state," said Echols, board president of the Economic Opportunity Foundation in Kansas City, Kan. "His bipartisan accomplishments have preserved our natural resources, protected worker pensions and extended educational opportunities to thousands of Kansas kids."

However, former state Rep. Charlie Roth, a Salina Republican who left office in 2012, said Davis had demonstrated at the Capitol the capacity to develop consensus on legislation important to Democrats and Republicans.

"Even though he was in the minority party, he engineered the bipartisan passage of several key pieces of legislation — including the state budget — during a very difficult time for our state’s economy," Roth said.

Fred Gatlin, who represented northwest Kansas in the House for nearly a decade and serves as co-chair of Republicans for Davis, said he was troubled "by the direction our state is headed."

"Kansans deserve a governor who will bring people together — someone who will make government run efficiently and work for everyone," he said.

David Kensinger, a former chief of staff to Brownback and organizer of the governor's re-election campaign, said voters of Kansas wouldn't support a candidate in November who served as a Barack Obama delegate at the 2008 and 2012 national conventions.

"There are only so many Kansans willing to vote for a guy who doubled down on the Obama agenda," Kensinger said.