Senate Majority Leader Harry Reid perked up some ears last week when he told Gannett News that Congress will follow up on the post-election agreement between President-elect Barack Obama and Sen. John McCain to move forward on reforming immigration laws.

We weren’t in the room when those erstwhile rivals met, but hallelujah, if that’s what they agreed to do. States like Texas and cities like Flower Mound live daily with Washington’s failure to create saner immigration laws, including a temporary guest-worker program and a way for illegal immigrants to earn citizenship.

What worries us is that this task may be more of a battle than Mr. Reid envisions. The Nevada Democrat says he doesn’t expect “much of a fight at all.”

True, some circumstances have changed since the Senate failed to overhaul immigration laws in 2006 and 2007. For one thing, there are fewer illegal workers because of stronger enforcement of our borders and our economy’s retreat.

But let’s not kid ourselves. Obstacles remain.

Interestingly, the bigger ones could come from the left, rather than the right. In the Senate’s previous debates, labor, civil libertarians and other parts of the Democratic left were content to largely let the Republican right kill the reform effort.

Now Democrats run Washington, and Mr. Reid must fend off his left flank if immigration reform is to have any meaning. That includes ensuring that labor doesn’t sharply restrict the number of guest workers, which union leaders quietly tried to do in 2007.

Another obstacle is the economy. Mr. Obama must balance various constituencies as he lines up votes for his economic plans. That includes winning Republican votes, which are needed so partisanship doesn’t overrun efforts to stabilize the economy. Getting them could be made trickier if Mr. Obama presses too hard on immigration.

That said, Mr. Reid’s comments encourage us. Certainly, Mr. Obama needs to deliver. He handily won the Hispanic vote, largely because Latinos considered him the stronger champion of fair immigration laws. He has a tricky task ahead, but we all have a stake in him making good on his promise.