Democrats have long pooh-poohed the idea that President Obama was in any trouble in Pennsylvania this year. The president romped in Pennsylvania four years ago, and the Democrats’ registration advantage seemed likely to offset any problems that might arise from a new voter ID law that (at least before a judge prevented its enforcement this year) threatened to make it a little more difficult for the party’s Philadelphia machine to observe a time-honored city tradition and cook the results. But it’s starting to look as if their confidence was misplaced. Despite the fact that the most recent state polls there were published last week, before the first presidential debate that has altered the dynamic of the race in Mitt Romney’s favor, both Siena and Susquehanna showed the president holding only a slim lead of either two or three points. That sets up Keystone Democrats for a rude awakening the next time the state is polled, though they got a foretaste of what that might mean with the publication of the latest poll in the state’s U.S. Senate race.

A Susquehanna poll published today shows incumbent Democrat Bob Casey just two points ahead of Republican Tom Smith. Casey is a popular, though lackluster, incumbent whose father (a longtime governor) is still remembered with affection, and no one believed he was in any danger of losing this year. That was certainly the case when the best the GOP could do to oppose him was Tom Smith, a Tea Party stalwart with little name recognition. The point here is that if Tom Smith is that close to Casey, the Democrat ticket in Pennsylvania may be far weaker than pundits, who have been painting the state dark blue in electoral map for months, thought. If Obama must fight hard for Pennsylvania — which has just been shifted into the tossup column by Real Clear Politics — his campaign has made a terrible miscalculation.

The closeness of the Senate race is due in large measure to Casey’s incompetence as a candidate. He won in 2006 almost by default against a deeply unpopular Rick Santorum, and got away with running what was widely considered a stealth campaign in which the nominally pro-life and pro-gun Democrat sought to avoid being pinned down on any issues. He’s trying the same trick this year, but in the absence of a highly visible opponent like Santorum, it isn’t playing as well. However, even Casey, who has one of the lowest profiles of any statewide political figure but very high name recognition, still ought to be having an easy time winning a second term against Smith. That Casey couldn’t maintain the double-digit lead he had over Smith most of the year is telling not only about his own problems but what it says about the weakness of the Democrat ticket.

The smart money will probably still be betting on Obama and Casey winning in November, but the news here is that they are going to have fight hard to do so. Republicans had hoped to make the president play defense in a state that was thought to not really be in play, and it appears they have succeeded in that quest. A determined Republican challenge in states like Michigan, Wisconsin and Pennsylvania doesn’t mean the Democrats can’t also fight hard in swing states such as Florida and Virginia that Romney must have if he is to win, but it makes it harder for them.

But that’s putting these results in what must be seen as the most positive light for Democrats. The nightmare scenario for Obama is that not only has Pennsylvania reverted to its pre-2008 status as a competitive if blue-leaning state, but that it is genuinely in play. Even scarier for them is the prospect of a spiraling Obama dragging Casey down with him. A few more polls like this and such an outcome will no longer be viewed as a GOP fantasy.