A hoary old adage about the weather is often attributed to Mark Twain: if you don’t like it now wait five minutes and it will change. Something like that has happened to the burgeoning reelection campaign of Pennsylvania’s Bob Casey now running for a third term to the U.S. Senate.

Only a few short weeks ago the expected Casey race looked like a ho-hum affair in which the popular Senator, bearing the iconic Casey name, would sweep to re-election against whatever sacrificial lamb the GOP served up to contest him. After all, Casey has run five times statewide for three separate offices in the past 15 years, winning all in a landslide.

Moreover, his 2018 candidacy going back to his father, the near legendary governor of the same name would be the 15^th time the Casey name had appeared on a state ballot over some six decades.

But then along came Lou – as in Congressman Lou Barletta (R), the Republican incumbent in Pennsylvania’s 11^th Congressional district – and everything changed. Casey’s scheduled walk-through became a possible marathon and one of the safest Democratic seats in the U.S. Senate suddenly looked competitive.

Lou Barletta is a competent, likeable congressman who entered politics as a small town mayor, parleying that into a congressional seat by advocating controversial, albeit wildly popular policies to combat illegal immigration.

He now sits in one of the most gerrymandered seats in one of the most gerrymandered states, and hence a seat he could probably occupy for life if he chose. Yet, he instead chooses to give that up, enter what looks like a testy GOP primary, armed with a war chest of only about a half million dollars and low statewide name recognition.

He does so for one compelling reason. His mere presence in the race will transform it into a direct referendum on Trump. That’s because Barletta was Trump before Trump was Trump.

In fact, one source has referred to Barletta as Trump’s “political Godfather” owing to his early high profile efforts to stem illegal immigration. Barletta was also one of the very first publicly to support Trump’s long shot presidential run, and he has been one of Trump’s strongest supporters in office.  He was briefly a candidate for two different cabinet posts and introduced a bill to help fulfill Trump’s campaign promise to build a wall along the U.S. Mexican border. Trump and Barletta are joined at the hip.

Meanwhile, Casey has become the “un-Trump,” transforming himself into one of Trump’s harshest critics. With the notable exception of trade policy, Casey has emphasized his opposition to Trump across the board. Moreover, this is a referendum Trump apparently wants as he has publicly and privately encouraged Barletta to get into the race. Trump is in it to win it, as they say.

But is it winnable? Can a relatively obscure congressman from rural Pennsylvania bring down the reigning colossus of Pennsylvania state politics? Probably not. Some commentators have taken to characterizing Barletta’s task as a “high hill” to climb. But the more apt metaphor is probably “a bridge too far.” Money will be his first problem. Currently, Casey has about ten times more cash on hand ($5.5 million). But even that will be ante up money in 2018. The Toomey race in 2016 topped $176 million, setting a national record. It’s possible that 2018 will exceed that.  Barletta has little experience in raising these magnitudes.

While Trump will aggressively support him, Senate Republicans will be less generous, committing national funds to races supported by leader McConnell and considered more winnable.

Nor will Trump’s low approval ratings in the state help Barletta. Certainly much of Trump’s core 2016 constituency still supports him. But with Trump’s approval rating hovering around the mid 30’s, will they go to the polls November 6^th to support Barletta.

Conversely, Casey enters the race with an enormous 800,000 plus active voter registration edge statewide including huge majorities in vote-rich Philadelphia and Pittsburgh. And Barletta will struggle against Casey on the vital trade issues so resonant in the state. Casey has carefully built his image as an advocate for fair trade policies and a critic of many free trade policies.

Similarly, Casey has minded the home fires, devoting much time to town halls interacting with ordinary folks. Also, he maintained a reputation for responsiveness to constituency service. While long considered a low profile campaigner, Casey has become a skilled debater and a competent speaker. In addition, he is mostly inoculated on the ever-bitter issues in Pennsylvania of abortion and guns. Both pro-life and pro-second amendment he incurs few of the handicaps in rural regions of the state experienced by most Democrats.

Finally, a statistic supplied by Larry Sabato at the University of Virginia spells out Barletta’s challenge: For more than a century, the reelection rate for incumbent senators of the party not in the white House is 91percent. Statistically speaking, that makes Barletta’s chances of beating Casey about nine percent.

That’s better than no chance – but not much better.