The House is expected to vote overwhelmingly Tuesday to override President Bush’s veto of legislation funding $23 billion worth of water projects, diminishing Bush’s authority as he heads into a spending showdown with Democrats over 12 unfinished appropriations bills, say government scholars.

A House GOP aide predicted a “99.99 percent” chance that the House would vote to override Bush, an outcome made likely by the 381 votes that the Water Resources Development Act (WRDA) received before reaching the president’s desk.

Republican leaders have not whipped lawmakers to vote against the bill in the House, even though Minority Leader John Boehner (Ohio), Minority Whip Roy Blunt (Mo.) and Republican Conference Chairman Adam Putnam (Fla.) all voted against the legislation in August. Senate Republican leaders are also not expected to twist arms to sustain Bush’s veto when the issue reaches their chamber later this week.

It would be awkward for Republican leaders to inveigh against the water bill, because so many members of their party support it for the millions of dollars’ worth of projects promised for their districts and home states.

The first veto override of Bush’s tenure signals the first time Republicans have deserted their president en masse, albeit on a relatively obscure issue. Congressional scholars say the rift between Bush and the majority of the party will diminish him as he prepares to battle congressional leaders over spending priorities. But how much authority Bush will lose, and how much of a wedge the bill will drive between GOP lawmakers and Bush, is a matter of disagreement.

“Once that crack in the unified front has emerged, it’s a little easier to have that happen the next time around,” said Norman Ornstein, a congressional scholar at the American Enterprise Institute. “Once Democrats are able to pull up enough votes to override something, it dilutes a little the veto threat.”

Bush’s expected defeat on the water bill raises questions over whether congressional Republicans will support his threatened vetoes of several appropriations bills.

“Coming at this particular point, where he hasn’t vetoed any spending bills in the past, it certainly makes him look weaker than he would have been,” said Paul Light, a professor of public service at New York University’s Wagner School.

Earlier this year, Bush vetoed legislation providing supplemental funding for the wars in Iraq and Afghanistan. He did so, however, because of a disagreement with Congress over curbs on his power as commander in chief, not because of a spending dispute. Bush also vetoed legislation expanding the State Children’s Health Insurance Program by $35 billion over five years. Bush argued the bill would lead to government-run healthcare.

Light said that Bush does not have a persuasive track record opposing spending legislation, noting that he has issued only a “handful of vetoes” and that the override comes late in his administration, when many in Congress are looking to the 2008 presidential election.

“This sets the precedent on spending bills,” said Light. “If he can’t sustain, one imagines Congress will up the ante with more projects in the next big bill.”

John Sides, a professor of political science at George Washington University, said the large number of Republicans expected to vote to override his veto could give Bush pause before vetoing future spending legislation.

Sides said that now is the time of year when “Congress routinely coalesces around big, overstuffed appropriations bills. It’s always risky to go against Congress when that’s been accomplished.”

House Republican leaders, however, predict they will be able to sustain vetoes on any of the annual spending bills this fall. They cite a letter sent to Bush in May signed by 147 Republicans pledging to sustain a veto of any appropriations bill exceeding Bush’s budget request.

“The Republicans have enough signatures from members of Congress pledging to uphold any veto, which they didn’t have on the WRDA bill,” said Brian Riedl, senior budget analyst at the conservative Heritage Foundation. “It would not create public confidence in Congress to publicly sign a pledge and publicly walk away from it.”

House Republicans argue that the water projects bill does not warrant the same level of loyalty to the president because it is merely an authorization bill. It grants authority for new projects but does not actually allocate funding.  

It appears White House officials are granting their fellow Republicans a tacit pass on that argument.

Sean Kevelighan, press secretary for the White House Office of Management and Budget, also noted that the water bill is “an authorization.”

“Not one penny of projects will necessarily be appropriated in the immediate future,” he said. “They still have to go through the appropriations process. Congress may be making promises they can’t keep to their constituents.”

But that argument does not wash with policy analysts, including conservatives at the Heritage Foundation.

“The authorizing bills are the first step in spending increases,” said Riedl. “The authorization bill could put a solid cap on spending by limiting the amounts. By not putting [on a] cap, authorizers are making it easier for appropriators to increase spending by fully funding all of these projects.”