WASHINGTON -- Sen. Bob Casey, a Democrat from Pennsylvania, lives along so many fault lines of American politics that he is especially sensitive to Trump tremors, which he fears could become an earthquake by November.

“I’m concerned,” he said. “Beating Donald Trump won’t be as easy as it might look.”

Casey is a pro-life Roman Catholic with a pro-gun history until recently, in a state that Democratic consultant James Carville once described as “Pittsburgh and Philadelphia with Alabama in between.” He is also an old-school Democrat and a new-school one: He's pro-union and wary of global trade; he defends Social Security, Medicare, Obamacare and same-sex marriage.

The mix works: Casey won re-election in 2012 -- the first Democratic senator in Pennsylvania to do so in half a century -- and ran well ahead of President Barack Obama that year. So he knows his people.

In Casey’s view, presumptive (if weakened) Democratic nominee Hillary Clinton will do well in Philadelphia and some of its suburban counties, and probably on his own home turf of Scranton in the state's hardscrabble northeast.

“The problem will be out west,” he said, where what used to be called Reagan Democrats live in large numbers in cities and towns that have never recovered from economic recession and off-shored industrial jobs – and where resentment of Washington and the coastal establishment is as much a part of the terrain as coal seams and forests.

“We’ve got to take Trump seriously,” said Casey.

Indeed you do, senator.

Here are seven reasons why Donald Trump could actually become president:

"It's the Economy, Stupid." That's another famous Carville dictum (from Bill Clinton's 1992 campaign).

It could sum up Trump's chances, too. Start with Casey’s concern about those towns out “west,” and add not only the well-documented stagnation of America's middle class but the possibility of another economic slowdown.

The rise of Trump could itself cause market tremors – it may already be doing so – but that won’t make it any less difficult (if not impossible) for Hillary Clinton to avoid being cast as the “incumbent” defender of the Obama economy.

Joe Raedle/Getty Images What will Bernie's supporters do in November?

Divided Democrats. Sen. Bernie Sanders is determined to carry his crusade through to July's Democratic convention in Philadelphia and to play the role that another failed candidate, the late Ted Kennedy, played in 1980 in New York: the star of someone else’s show. Kennedy’s dramatic farewell stole the moment from a sitting president, Jimmy Carter, and presaged Carter's loss to Ronald Reagan.

The dispirited Kennedy clan rallied, reluctantly, to Carter in the end because they still had a residual sense of loyalty to the party they had long dominated. But the Sanders crowd has no such loyalty, and their leader is not even a member in good standing of the Democratic Party. What’s more, the power of social media means that his troops can do what they wish by caucusing among themselves, no matter what Bernie says.

Republican Weakness. Some Republicans and conservative commentators, such as The New York Times' David Brooks, are warning Republicans that they face a “Joe McCarthy Moment,” in which they must repudiate Trump or risk the wrath of history’s judgment. And some Republicans are still vowing never to back Trump.

But GOP leaders such as Chairman Reince Priebus are more interested in immediate peace than their place in history, and amenable characters such as former Utah Gov. Jon Huntsman have said that nominating Trump is no big deal.

The GOP failed its last “Joe McCarthy moment.” It was Sen. McCarthy’s own persona, as displayed on a newfangled thing called broadcast television, that brought him down -- not his fellow Republicans.

Will Sen. Ted Cruz, who suspended his campaign Tuesday night, urge his evangelical minions to abandon the GOP this November? Nah. He will pipe down and hope to pick up the pieces in 2020.

Journalistic Weakness. It comes in two flavors. One is false equivalence. Reporters have yet to fully examine Trump’s record, especially the details of his business dealings and personal life, but soon enough his story will be yoked with and compared to Clinton’s, which will make it easier for Trump to slide by in the resulting din.

The second flavor is the media's hunger for an audience. The closer Trump gets to the White House, the more frightening he becomes, the more desperate his enemies become – the more eyeballs are focused on smartphones and TV sets.

That means more billions in “free” media for Trump.

Joe Raedle/Getty Images Hillary Clinton still looks good for the Democratic nomination, but after that, the road gets rockier.

Hillary the “Incumbent.” As much as Clinton talks about new ideas and a fresh start, she will be attempting the difficult task of holding the White House for the same party for a third-straight term. That last happened in 1988.

More important, Clinton and her husband represent a force in the Democratic Party that is a kind of incumbency within an incumbency, and that is a perilous place to be at a time when voters so despise Washington.

“There are reasons why a 74-year-old socialist from Brooklyn is doing so well,” said Tad Devine, Sanders’ media adviser and friend for decades. “The level of dissatisfaction with the establishment is sky high, and she is a symbol of it.”

Not surprisingly, Trump is now claiming Sanders as a sort of ally. Will the senator cry foul and unleash his fury on Trump? Even if he does, will his supporters agree?

Trump Turns. The flip side of having no voting record and no consistent views is that you can reshape your positions at will to suit the moment. Watch Trump, the master huckster, play more to the social middle from here on.

It’s cynical but cunning, and it could work. The bar for him is so low, the expectations are so low, that Trump has a lot of freedom to move.

The Numbers. Shockingly – given his outrageous, race-baiting and even violence-tinged rhetoric – Trump is not that far behind in the horse race as the “fall” campaign informally begins.

Nor does the Electoral College map look that impossible for him. With the possible exception of Arizona, there are few, if any, red states from 2012 that he would likely lose.

There are also at least five large blue states in which he could compete, especially for the votes of those former Reagan Democrats. Those states are Florida, Ohio, Virginia, Wisconsin and, yes, Pennsylvania.

Together, they represent more than enough electoral votes to send Trump to the White House.

Bob Casey will be working hard to keep his state out of Trump's column, but there are no guarantees.

Editor's note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims -- 1.6 billion members of an entire religion -- from entering the U.S.