As Congressional Democrats rally around Sen. John Kerry’s candidacy for president, Republicans are preparing a plan that would force the Massachusetts Democrat to vote on politically sensitive issues, including judicial nominees opposed by powerful Democratic constituent groups.

Republicans see this as an opportunity to either win approval for more of President Bush’s judicial picks or, at the very least, paint Kerry and his Democratic colleagues as partisans interested solely in political gain.

For the past three years, Republicans have directed the obstructionist charge primarily at Senate Minority Leader Tom Daschle (S.D.), the titular head of the Democratic Party since Bush was elected in 2000. But with Kerry likely to win the Democratic nomination, Senate Republicans are prepared to shift most of this criticism to the Massachusetts Democrat, who they claim is complicit in the strategy to block Bush’s picks for the federal bench as well as slow-walk major components of the Republican agenda.

“The reality of this is that Senate Democrats have made the Senate the stage for their party definition,” said a Republican leadership aide. “When John Kerry comes back, we will make it the stage to define him as well.”

Republicans are setting their sights on Kerry, judging that his near-perfect track record in the nominating contest and his endorsement by the AFL-CIO last week makes him the likely Democratic choice to challenge Bush in November. They are now crafting a plan to discredit the Senator by focusing on his legislative career.

Republicans said they believe the issue of Democrats blocking Bush’s judicial nominees is resonating with voters, and forcing Kerry to vote to block confirmation of a federal judge would hurt him politically, particularly in swing states where such judicial vacancies exist.

“The Democrats have made this a political playground, and when Kerry is their nominee we will play in that playground too,” the GOP leadership aide said.

Democrats successfully used parliamentary tactics in 1996 to help derail then-Senate Majority Leader Bob Dole’s candidacy for the White House and in the process forced the Kansas Republican to resign his seat — a fact that Republicans have never forgotten.

“Those who were around in ’96 have found what Democrats did to Bob Dole distasteful,” said a senior Republican aide.

In addition to votes on judicial nominees, Republicans are scouring his voting record in search of inconsistencies and plotting how best to use the Senate to echo the White House bully pulpit.

“There are a lot of available bear traps in the Senate,” the Republican aide said.

Michael Meehan, a senior Kerry adviser, said the campaign was not surprised that Republicans are preparing an all-out assault on the Massachusetts Democrat.

“Given the fact there are a dozen national polls in the last five weeks that show John Kerry beats George Bush, I would expect that every Republican in Congress, like every member of the Bush campaign team, are terrified and will do everything to stop him,” he said.

But questions remain about whether Kerry will return to work in the Senate this year or instead focus his full attention on trying to win the White House. So far Kerry has missed all 14 Senate votes this session, as has Sen. John Edwards (N.C.), who is also seeking the nomination.

Several of his Democratic colleagues said they would advise Kerry to stay on the campaign trail and avoid the unpredictable Senate schedule.

“You have to take your case to the people, and the best place to take the case is to be as close to the people as you can,” said Sen. Dianne Feinstein (D-Calif.).

“If I were him, full steam ahead,” said Sen. Joseph Biden (D-Del.). “I don’t think [spending time in the Senate] matches being on the trail.”

The Senate, though, would offer Kerry a convenient soapbox where his mere arrival on Capitol Hill to deliver a speech from the floor would draw serious media attention. As for taking the lead in the Senate on important legislative issues such as minimum wage or education, Sen. Edward Kennedy (D-Mass.) noted, “Anything is possible.”

Still Kennedy, Kerry’s closest ally, suggested that his junior colleague would spend little time in the Capitol this year. “But the next major speech I expect from Kerry delivered to the Senate will be his first State of the Union address.”

There is historical precedent for the Democratic leadership to hand over substantial control of their agenda to a Senator who is also the Democratic presidential nominee. In 1960, then-Senate Majority Leader Lyndon Johnson (D-Texas) empowered then-Sen. John Kennedy (Mass.) — the Democratic presidential nominee — to run the floor in a brief session following his party’s political convention.

“Johnson stepped aside to allow Kennedy to manage the bills,” said Don Ritchie, the associate Senate historian.

Ritchie noted that Kennedy was viewed as a backbencher and was “so junior he didn’t have a hideaway office.” This was rectified when then-Majority Whip Mike Mansfield (D-Mont.) offered him space in his Capitol office.

As for Kerry, Meehan said the game plan regarding votes and the Senator’s presence in the chamber hasn’t changed since he launched his bid for the White House.

“As Kerry has done for the last year of the campaign, if his vote is required and close enough he will be there for it and he will continue to do that as the election goes forward,” Meehan said.