Republicans and Democrats don't agree on much these days, but if there's any point on which they should still see eye to eye it might be the federal earned-income tax credit.This cash supplement to wages, delivered in the form of a tax refund, was created during the Ford administration and has been gradually expanded under Republican and Democratic presidents. In 2012, it totaled $63 billion, paying an average of $2,300 to households containing 27 million people.The EITC subsidizes low-income workers who make the effort to find a job and the employers who hire them without wasting benefits on middle-income teenagers and other non-poor workers, as the minimum wage does. Indeed, growth in this tax credit offset much of the minimum wage's inflation-adjusted stagnation in recent years.Many conservatives have cited the tax credit, correctly, as a more efficient, market-oriented approach to fighting poverty and inequality than the minimum wage, which Democrats have been seeking to raise.So how come the new tax reform plan from the top Republican tax-law writer in Congress, House Ways and Means Committee Chairman Dave Camp, would reduce the credit by $48.2 billion between 2015 and 2018 and use the savings to help pay for a plan that lowers marginal tax rates, including for the well-off?Camp's proposal would reduce the current maximum EITC benefit, from $6,143 for a two-parent family with three or more children, to $4,000 for a two-parent family with two or more kids. And it would reduce the credit's already inadequate coverage of childless single workers by cutting their maximum benefit from $487 to $100.Camp's plan quickly came under fire from Robert Greenstein of the liberal Center on Budget and Policy Priorities, who noted that it could cost a single parent with two children who works full time at the minimum wage about $350 in 2018 compared with current law.In Camp's defense, differently configured households might fare better than Greenstein's example; he mitigates the changes to the EITC with a considerably more generous child tax credit, which is also linked to wages and, therefore, work effort. Overall, his plan would slightly reduce taxes paid by those at the low end of the income distribution spectrum.There is a genuine issue with the current program: Its complex eligibility criteria, and poorly regulated filing process, lead many people to claim, and get, more money than they should — between $11 billion and $13 billion in 2012, according to the Treasury Department's inspector general, and more than $130 billion over the past decade. Much of that was due not to good-faith error but to cheating by tax preparers, whose fees often depend on the size of the refund or who lend money to clients in anticipation of their checks.Camp would attack these overpayments — much of which are pocketed by the go-betweens, not the low-wage workers anyway — by converting the earned-income tax credit into a rebate of an employee's Social Security taxes. According to a Joint Committee on Taxation summary of the provision, this "is both much simpler and more transparent than current law, with the potential for fraud reduced by the direct link to payroll taxes withheld on a taxpayer's Form W-2."The idea is clever and politically daring — maybe too daring, because it could be construed as raiding a revenue stream dedicated to the Social Security trust fund. That fund is an accounting fiction, but it's a widely cherished accounting fiction.Meanwhile, some 22 percent of potentially eligible workers never file for the EITC because of the program's daunting complexity, Treasury's inspector general has found. Camp's simplification might encourage more of them to sign up.Camp's lower EITC benefits per household were meant at least partly to allow for an increase in participation while keeping the overall impact of tax reform revenue-neutral.Still, he wouldn't have had to do that if not for other provisions in his plan that mainly benefit corporations or the wealthy, such as eliminating Obamacare's medical-device tax or maintaining the preferential treatment of investment income for top earners.A better approach would be to use the proceeds from reducing overpayments to maintain an earned-income tax credit at least as generous as it is now, on a per-recipient basis. If overpayment-reduction isn't enough, then the money should come from somewhere else.Camp deserves credit for taking on tax code sacred cows, such as the deductions for mortgage interest and state and local taxes that mainly benefit upper-incometaxpayers.In dealing with the earned-income tax credit, however, the Ways and Means chairman had a chance to show GOP seriousness about market-based approaches to the plight of low-income Americans — and didn't quite make the most of it.Lane is a member of The Washington Post's editorial board.