By Kathleen Hunter, CQ Staff

With two of their own squaring off for the White House, Democratic and Republican senators have been working hard to coordinate their election-year messages with presidential campaign politics.

On Thursday, Senate Democrats will turn to a new page in their offensive playbook.

Majority Whip Richard J. Durbin — Illinois’ senior senator and presumptive Democratic nominee Barack Obama ’s most stalwart Senate surrogate — will headline what is likely to be the first of many news conferences intended to poke holes in the Senate record and campaign-trail proposals of Republican White House hopeful, Sen. John McCain of Arizona.

The event will focus on McCain’s tax proposals. Durbin and others will release a report indicating that McCain’s tax plan would amount to an additional $300 billion annually in tax breaks and would funnel billions of dollars to Fortune 200 companies.

Senate Republicans aren’t cowed by the move.

“Good — I want people to compare the policy differences between senators McCain and Obama,” said South Carolina Republican Lindsey Graham , McCain’s closest Senate ally, when asked about Thursday’s event.

“On taxes, one guy’s going to try to raise everybody’s taxes. One guy’s going to try to keep them low . . . Republicans love cutting taxes. Democrats love spending . . . The Democratic budget will be a centerpiece of our campaign,” Graham said.

Two Democratic senators from key battleground states — Pennsylvania’s Bob Casey and Minnesota’s Amy Klobuchar — will join Durbin and James Kvaal, a senior fellow at the left-leaning Center for American Progress Action Fund, at Thursday’s event.

GOP senators, for their part, have taken every recent opportunity to slam Obama’s policies and rhetoric on gas prices, energy and the economy, the last of which they have begun to call derisively “Obamanaics.”