It has become almost a cliché for Republican candidates to admit that their party “lost its way” on spending and the size of government during the Bush era. But with the GOP poised to retake the House and possibly even the Senate this November, it is worth pondering whether they really understand why voters turned against them in 2006 and 2008.

Exhibit No. 1 is earmarks. Few issues were as symbolic of the Republican abandonment of conservative principles. When the GOP took over the House in 1994, the federal budget contained fewer than 2,000 earmarks. By the time voters threw the Republicans out in 2006, there were 9,963. And that was down from nearly 14,000 the year before. It is worth remembering that Ronald Reagan once vetoed a highway bill because it contained 152 earmarks, which he called “a textbook example of special-interest politics at work.” Twenty years later, Republicans managed to put together a highway bill that contained 6,371.

Last year, responding to grassroots demands for fiscal discipline, House Republicans imposed a one-year moratorium on requesting earmarks. And they’ve mostly been faithful to that promise. Since the ban was adopted, Republicans have asked for only seven earmarks. But with that moratorium expiring, they seem to be slouching back toward politics as usual.

It is particularly troubling that the GOP’s new Pledge to America contains no mention of earmarks. Given the current political climate, one would think that a pledge to end earmarks would be a clear winner. Its absence suggests that Republicans have no intention of sticking to the earmark ban.

In fact, House minority whip Eric Cantor, the No. 2 member of the House Republican leadership and a leader of the supposedly more fiscally conservative “young guns,” has said that a GOP-led House would be willing to allow earmarks next year “as long as the spending items have merit.” That caveat is not exactly reassuring. Is there any member of Congress who doesn’t believe that his particular boondoggle has “merit”?

Cantor’s boss, John Boehner, who commendably has eschewed earmarks for his own district, has pointedly refused to contradict Cantor or make a firm commitment to extend the earmark moratorium. Others, such as Rep. Jerry Lewis (Calif.), who will likely take over as chairman of the Appropriations Committee if the Republicans regain a House majority, are positively salivating at the prospect of being able to earmark once again. “I think that members have the right to represent their constituents,” says Representative Lewis in defense of bringing home the bacon. In the year before the Republicans imposed their moratorium, Lewis secured 50 earmarks for his district at a cost of $82 million.

Of course, some might wonder why banning earmarks is important. After all, they are only a tiny fraction of federal spending. All earmarks combined this year amounted to just $16 billion out of a $3.72 trillion budget. Earmarks accounted for just 1.2 percent of federal discretionary spending.

But earmarks have an impact far beyond their cost in dollars. First, they have been a major source of congressional corruption. Many of the scandals that beset the last GOP Congress were the result of earmarks. Remember Duke Cunningham and Jack Abramoff? The corruption continues, of course, under the current Democratic Congress. The FBI is reportedly investigating several instances in which congressmen allegedly traded earmarks for campaign contributions. Why would Republicans want to wade back into that swamp?

More insidiously, earmarks are part and parcel of the deal-making and horse-trading that greases the skids for so much bad legislation in Washington. Vote against the leadership’s pet legislation and your earmark gets cut off; vote for it and your district gets some delicious pork. And nothing helps an otherwise terrible bill gather votes better than stuffing it full of earmarked goodies for wavering lawmakers. Therefore, even a very small earmark can be used to leverage far more costly government spending.

Moreover, earmarks fly in the face of the GOP’s newly discovered reverence for the Constitution. Even if one concedes Congress’s power to spend money on earmarked projects, that power is still constrained by the general-welfare clause, which requires Congress to exercise its enumerated powers for the “general welfare” of the population. It is hard to claim that refurbishing a theater in some congressman’s district or building a “bridge to nowhere” is contributing to the general welfare.

Earmarks are also bad economic policy. A study earlier this year by Lauren Cohen, Joshua Covel, and Christopher Malloy of Harvard Business School concluded that earmarks crowd out local private-capital investment and research-and-development spending, thereby slowing economic growth.

Finally, there is much to be said for the biblical injunction “He that is faithful in that which is least is faithful also in much: and he that is unjust in the least is unjust also in much.” If Republicans can’t end earmarks, how can we expect them to make hard decisions when it comes to something like entitlements? (Come to think of it, that’s another area where the Pledge to America remains unsettlingly silent.)

Republicans should do very well this election cycle simply by not being Democrats. But that doesn’t mean that they have earned back the public’s trust. In fact, polls consistently show that voters’ opinion of the Republican party is dismal, even as they plan to vote for GOP candidates.

If Republicans slip back into the bad old habits of the past, they may find this year’s electoral success to be fleeting.