Not anymore. Since the start of the week, four reputable firms have released new surveys–and all of them show the gap narrowing significantly. SurveyUSA says Clinton is beating Obama by 12 points (53-41), down from 19 on March 10. Quinnipiac pegs the margin at nine points (50-41), even though the sample started last Monday; its previous poll, released on the 16th, had Clinton ahead by 12. Meanwhile Obama has cut Clinton’s lead in the Rasmussen survey in half over the last week, from 10 points to five, and new numbers from Public Policy Polling go so far as to put Obama ahead by two (45-43). Clinton’s advantage in PPP’s March 16 poll? Twenty-six percent. Her average edge is now down to six points. Which has observers asking whether Clinton could actually lose Pennsylvania–an outcome that would vastly increase pressure to end her White House bid.

It’s a bit early to declare doomsday (to put it mildly). After all, the PPP poll is the first not only to show Obama leading–it’s the first to show him within the margin of error. As such, it has to be considered an outlier until other surveys substantiate its unprecedented findings. That said, PPP has established a pretty impressive predictive record over the course of the 2008 primary season. In South Carolina, the firm was among the first to foresee Obama’s larger-than-expected blowout. Its final Wisconsin survey (+13 for Obama) came closer to matching his actual margin (+17) than any other poll. And it was one of the few outlets to correctly pick Clinton in both the Ohio and Texas primaries. So it’s no slouch. In any case, it appears that over the past week or so, Obama has slashed Clinton’s once commanding lead in the Keystone State by a third to half. End of story.

Experts credit two recent events for Obama’s rapid rise: 1) last week’s endorsement from pro-life, Irish Catholic Sen. Bob Casey, Jr., who, as the son of a former governor, is popular with Pennsylvania’s massive population of white, working-class (and typically pro-Hillary) “ethnics” and 2) Obama’s six-day, down-to-earth Pennsylvania bus tour, which wraps up tonight in West Chester. The former, says Franklin & Marshall political expert Terry Madonna, “threatens to undercut Clinton’s support with some key constituencies, especially blue collar, working class, white voters, many of them Catholic, who so far have been hot for Hillary but only lukewarm for Obama… [Casey] might persuade many of them to take a second look at Obama.” And the latter, with its unmarked bus, its bowling alleys, its hot dogs, its Yuenglings and its populist appeals at modest town hall meetings (rather than massive arenas) has earned Obama plenty of fawning local media coverage–just the thing, along with a $3 million ad blitz, to make the man with the “Muslim” name seem a little less alien to blue-collar voters. “I would be surprised if this doesn’t move numbers,” says Madonna.

Thanks to Clinton’s demographic advantages, Obama is still a serious long shot to win the Pennsylvania primary. But his budding surge should still worry her staffers. In state after state, as Team Obama is quick to note, the Illinois senator’s support gets stronger the more time he spends on the ground–and in this ra-ta-tat cycle, three weeks is an eternity. Like so many of the preceding primaries, Pennsylvania is as much about who wins the vote as who wins the expectations game. It’s silly but true. The problem for Clinton is that, with April 22 long established in Hillaryland as a must-win (if not a will-win), expectations are astronomical for Clinton and abysmal for Obama. As Madonna puts it, “she needs margins large enough to buttress her argument that only she can win critical Electoral College states like Pennsylvania, and margins large enough to allow her to harvest a significant proportion of pledged delegates to make some gains on Obama in that critical category.” In other words, Clinton wins only by winning big; a close finish may look like a loss. And right now it appears that the Keystone State is getting too close for comfort.