After more than four years of hand-in-glove legislative coordination between the White House and Congress, two high-profile bills seem certain to test this partnership over the coming weeks.

Despite veto threats from the Bush administration on both the highway bill and on legislation that loosens restrictions on stem-cell research, the House and Senate appear likely to adopt provisions deemed unacceptable to the White House, setting up a test of wills unusual in the recent era of Republican-controlled Washington.

The possibility of a presidential veto and the resulting fallout remain matters of considerable debates within GOP circles.

For some, a Bush veto — which would be the first of his presidency — is nothing more than the inevitable result of an age-old clash between the legislative and the executive branches.

“Congress and the president are like an overachieving student getting A’s for four years and then they get an A-minus,” said one House Republican leadership aide. “It’s no big deal.”

The Office of Management and Budget provided figures that showed through the end of May, the White House — either through the president, a senior adviser, or an agency — had issued 86 veto threats since 2001.

“The president has been fortunate that he hasn’t had to veto legislation, because he has been able to work with Congress on his priorities,” said White House spokesman Trent Duffy. “We will see what happens with stem cell and the [highway] bill.”

Other Republicans, however, see the disagreement as a sign that Congressional GOPers are beginning to distance themselves from a president whose poll numbers have been plummeting.

“The political climate for Republicans now stinks, and Bush is a part of that,” said a Republican consultant who spoke on the condition of anonymity. “Congressional Republicans are worried.”

It remains to be seen whether one or both of the pieces of legislation in question will force Bush’s veto pen.

The highway bill, which authorizes myriad transportation and road projects throughout the country, is currently in conference committee, with House Members and Senators seeking to hash out differences between their competing bills.

The House passed a measure authorizing $284 billion in funding, a figure consistent with the financial ceiling previously established by the White House.

The Senate bill, however, authorized $295 billion — by a largely bipartisan 89-11 margin.

Several Republican sources on Capitol Hill said privately that an acceptable compromise is likely on the highway bill, given the relatively small gap between what has been passed and what Bush wants.

“At the end of the day you are not going to see [Senate Majority Leader Bill] Frist [R-Tenn.] and [Speaker Dennis] Hastert [R-Ill.] bring spending legislation to the president that he is going to veto,” said one GOP Senate aide. “That would be a big repudiation.”

White House spokesman Scott McClellan echoed that sentiment Friday saying “there’s been good progress made” on the highway bill.

Late Friday, a deal appeared to be in the works for $286.5 million in funding — a figure still in excess of the Bush veto threat.

Even so, the administration’s hard-line stance on a bill that is popular among Members keen on delivering pork to their districts has left some in Congress perplexed.

“I don’t know anybody who has ever understood why the president dug in his heels on the highway bill,” said one Senate Republican aide. “This is a jobs bill. Members are going to fight for their districts.”

The debate over stem-cell legislation is considerably more complex and offers the most likely vehicle for Bush’s first veto.

The legislation, which would allow the government to finance studies of embryos that have been frozen in fertility clinics, passed the House 238-194 with the support of 49 Republicans.

The Senate Judiciary Committee will begin marking up the bill by the middle of next month and Frist has said he expects to bring the bill to the floor for a vote before the August recess.

Sources familiar with the House vote insisted that the legislation had a “groundswell” of support that the GOP leadership couldn’t stop despite the looming veto threat. “The stem cell bill was going to the president anyway,” said one House GOP leadership aide.

And, due to the decidedly personal nature of the bill, the Republican leadership did not whip the bill.

Given those realities, GOP lobbyist Charlie Black insisted that even if Bush ultimately does veto the stem cell bill, he should not expect any ill will to emerge between the two branches as a result of his actions.

“It is a philosophical disagreement,” said Black. “I do not believe it is one that will cause lasting hard feelings among Republicans.”

If Bush does exercise his veto on a stem cell bill, the House and Senate would need two-thirds supermajorities to override that decision.

Backers of the legislation in the House would need 287 votes — 49 more than they received late last month on passage — to overturn the president’s prerogative.

The increased willingness to buck the White House on policy proposals since Bush won a second term last November is due at least in part to the party’s successes at the ballot box, said one Senate aide.

“With larger majorities it is harder to keep everyone in line,” said the aide. “If somebody broke ranks a few years ago, you stuck out like a sore thumb.”

Since Bush ascended to the White House in 2001, Republicans have gained nine House seats and six Senate seats — enough for a majority that’s narrow by historical standards, but enough for a workable governing majority.

Due to Bush’s soaring popularity following the Sept. 11, 2001, terrorist attacks, Congressional Republicans tied themselves tightly to the president and his policies in the 2002 election.

As the president’s popularity waned in late 2003 and into 2004, Republicans continued to stick by Bush because “it was getting so close to the election that you have to sail with that ship,” in the words of one GOP strategist.

Now, with Bush certain never to stand for the presidency again and his favorability numbers at their lowest point of his tenure, Congressional Republicans appear to be growing more bold in highlighting differences.

“Members are now concentrating on 2006,” said one Senate Republican aide.