THE MOST ambitious plan to expand casino gambling since it was approved by Maryland voters in 2008 is on life support, a victim of the dysfunctional politics that has long plagued the issue in Annapolis. At the eleventh hour last week, members of the House of Delegates threw a wrench into the works of the proposed expansion, thereby delaying, if not derailing, a proposal to build a sixth casino — a big one in Prince George’s County — and to add table games to the five slots casinos already operating or authorized in the state.

The House members’ defection was a consensus-killer for a state panel commissioned by Gov. Martin O’Malley (D) to study the feasibility of expanding gambling in Maryland. The idea of expansion is driven by a desire to reap additional revenue and make the state’s casinos more attractive than their competitors in Pennsylvania, Delaware and West Virginia.

When it comes to gambling, no proposal is ever really dead in Maryland, and this one isn’t either. Pushed by the state Senate president, Thomas V. Mike Miller Jr. (D-Calvert), and by an array of other parties who find the revenue irresistible, expansion proposals will be revived sooner or later — though not necessarily in time to be considered in a special legislative session in July or placed before voters on the November ballot, as Mr. O’Malley had hoped.

Gambling, particularly slot machine terminals, is a toxic way for a state to raise money, as we have frequently argued. It amounts to a tax on the poor and the middle class, who patronize casinos though they can least afford it. It invites an array of social problems, including gambling addiction. And as the current fight illustrates, it is politically venomous.

Nonetheless, Maryland has moved past that debate. The questions now are how much gambling, and how many casinos, to allow. Here, too, there are reasons to proceed slowly.

The proposal for a huge gaming venue at National Harbor, on the Potomac River in Prince George’s County, would be a game-changer for Maryland’s existing casinos, especially the biggest one, Maryland Live!, which opened just this month near Baltimore-Washington International Marshall Airport in Anne Arundel County. The developers of Maryland Live! argue, with some reason, that their profits would be undercut by what Prince George’s officials envision as an $800 million casino located barely an hour’s drive away.

The idea was to soften the blow for Maryland Live! — and sweeten the pot for all the state’s casinos — by allowing table games such as blackjack in addition to the slot machines that have already been authorized, as well as by increasing the gaming firms’ share of the take by lowering their taxes. But the House members of the gambling panel balked.

It doesn’t much matter whether the delegates were reluctant to grant a tax break to gaming firms even as tax rates are rising for many Marylanders, as they said, or whether they merely wanted to protect Maryland Live!’s profit margins. In either case, a major gambling expansion lacks political support in the House for now.

There are reasonable arguments for a high-end casino at National Harbor, one that would generate revenue for the state and county by attracting tourists, convention-goers and well-heeled locals from Northern Virginia and the District. But before rushing to build it, the state should ensure that its three existing casinos, especially the just-opened, $550 million Maryland Live!, have a running start.