When it comes to open seat opportunities, Democrats are being handed all the right seats, but they might be coming at the wrong time.

Rep. Jim Gerlach is the latest Republican to announce his retirement in a competitive congressional district. Democrats have coveted Pennsylvania’s 6th District — along with districts such as Iowa’s 3rd, Virginia’s 10th, New Jersey’s 3rd and Florida’s 13th.

Just a couple of months ago, Democratic strategists would not have dreamed that all of those seats would open at the same time. But the midterm election dynamic, which could turn against President Barack Obama and his party, could dampen some of their enthusiasm.

When it comes to Gerlach’s district, Republican chances of holding the seat are buoyed not just by the president’s slumping job approval ratings, but by the last round of redistricting. Prior to the 2012 elections, Republican state legislators redrew the 6th District from a seat Obama won with 58 percent in 2008 to one where he took 53 percent.

In last presidential race, Mitt Romney won the 6th District, 51 percent to 48 percent, even though the former Massachusetts governor received only 47 percent statewide. In 2004, President George W. Bush won the district (as currently drawn) 53 percent to 46 percent even though he received 48 percent statewide.

Over the past decade, Gerlach proved to be a very formidable incumbent — a perennial target that Democrats could never oust. He was initially elected in 2002 and won his first three re-election bids with an average of 51 percent in very competitive races. Gerlach won his past two races with remarkably similar 57.1 percent to 42.9 percent margins each time.

Now that he is gone, Democrats will have a much better opportunity to take over the seat. It will likely be at least a few weeks before the candidate fields take shape, but Gerlach’s announcement fundamentally changes the dynamic of the race.

For now, we’re changing our Rothenberg Political Report/CQ Roll Call rating of Pennsylvania’s 6th District to Lean Republican from Safe Republican.