Barack Obama’s broad victory worked its way down the ticket, and was very good news for Democrats in New England, continuing the region’s transformation into a one-party enclave. Many years ago, New England was a GOP stronghold.

Since Democrats are arguably in the strongest position they have been since the “Great Society” era of Lyndon Johnson four decades ago, that should give New England greater clout in Washington starting next year. That’s especially so given the seniority of New England Democrats on Capitol Hill, who tend to be re-elected and re-elected and . . .

Democratic incumbents — including Sen. Jack Reed and Representatives Patrick Kennedy and James Langevin, in Rhode Island, and Sen. John Kerry and Rep. Barney Frank, in Massachusetts — coasted to easy victories. (Will Senator Reed, an authority on defense-related issues, be chosen for a position in the Obama Cabinet?) As noted in the editorial above, the last standing GOP House member in New England, “Rockefeller Republican” Chris Shays of Connecticut, went down to defeat, as did Republican Sen. John Sununu, of New Hampshire.

Voters in the Bay State wisely rejected an ill-considered measure to do away with the state income tax, and approved a measure to decriminalize marijuana. Rhode Islanders, for their part, voted to borrow more money for highway work and protecting open space.

Locally, one of the striking signs of a Democratic landslide was the fate of Republicans in the Rhode Island General Assembly. Already virtually an endangered species before Tuesday, they apparently lost eight of their 18 seats in the Assembly, as if voters were blaming this petite minority for the Rhode Island’s worst-in-the-nation unemployment rate and other economic woes. Such honest and good-natured representatives as Nicholas Gorham, a Republican from Coventry, fell in the onslaught.

As even union leader George Nee noted — perhaps wryly, since he was one of the architects of the phenomenon — it is unhealthy for any state to be so utterly dominated by one party. We agree. Competition tends to make better public policy, and reduces corruption.

Several factors weighed in the trend: GOP Governor Carcieri’s inept political maneuvering and party mismanagement; the state’s master voting lever, which lets voters choose one party up and down the ballot; and, of course, the general repudiation of Republicans.

One prominent Democrat, Senate President Joseph Montalbano, was ousted, brought down by ethics problems and a well-funded campaign by Lincoln’s Edward O’Neill, who as an independent was not tarred by the Republican brand. Senate Finance Committee Chairman Stephen Alves fell in the Democratic primary. Democrats must pick a new leadership team of leaders when they reorganize.

With such dominant power, of course, comes great responsibility. Though they do not control the governorship, Democrats cannot plausibly assert that they lack the muscle to change economic (including tax), education and other polices in the Ocean State to help lift it out of the doldrums. It’s their game.