To a pure optimist — and we don’t harbor many of those alien types in and around Philly — it’s a sexy, first-world idea: Build five miles of new train tracks to connect craggy rust-belt Norristown to gleaming King of Prussia, the gold-rush-hot zip code of commercial and retail redevelopment in the Philadelphia suburbs.

It’s what great societies do: They build infrastructure. And King of Prussia, a ballooning new-jobs nexus amid a tangle of suburban highways in our many-millions-strong region — could probably use some train love.

But to a realist, the scenario seems sketchy. And a realist with even a glancing knowledge of political and economic history in Southeastern Pennsylvania can come to only one conclusion about the $1.2 billion proposed extension of the Norristown High-Speed Line:

It has a snowball’s chance in you-know-where of coming to life.

For starters, it is no secret that this project is high on hopes and low on cash. It has no clear funding path despite big-bucks private-sector boosters calling for its construction.

But why? And how much of that can be overcome? For answers, I looked to the past.

I dug through news clips and interviewed some local transit experts, with decades of knowledge among them. What I found was confirmation of the worrisome hunch that got me started on this reporting journey — that there was something strange about the fact that I couldn’t remember a single new rail project in my adult lifetime.

My big discovery: No one has dropped new train tracks in Southeastern Pennsylvania in 34 years. SEPTA told me this, and The Inquirer’s news archives, too.

The last time we saw a rail project come to life was in 1985, when SEPTA delivered a completed stretch between Center City and Philadelphia International Airport.

That 9.4-mile-long project had been an ugly slog, though, in the works since the 1960s. Back in the Sixties, the federal government was far more generous to Democratic-voter-packed cities and suburbs. That this little old project experienced so much trouble is a cautionary tale about the realities of life here.

But wait, there’s more. The Republican president in charge when the Airport Line finally opened, GOP lion Ronald Reagan, added insult to injury — and in ways keeping us down still.

It was during the Reagan era that the feds decided they no longer wanted to be generous in helping finance rail projects.

No longer would the feds cover 80 percent for projects like the Airport Line. Instead, like a cheap blind date, Republicans decided that the best way to keep America great was to go Dutch on rail infrastructure. That made costly rail projects a lot harder to pursue in places that didn’t have a super-rich local or state tax base.

Of course, that means things were made worse for us by Republican majorities in Pennsylvania’s state House and Senate. Their retrograde tax policies have starved our urban and suburban localities of state revenue, forcing us to swallow higher and higher annual local tax bills to make up the GOP tax dodge.

“A billion dollars,” said Vukan Vuchic, legendary professor emeritus of transportation systems at the University of Pennsylvania, “where would that come from?”

If anyone thinks the way to finance the King of Prussia rail line is to tax the locals, a better idea might be to see a psychologist. Imagine if SEPTA had tried to do that in South Philly when, in the 1970s, it extended the Broad Street Line to the newly built stadium complex.

There would have been street riots. Count on it.

Vuchic works as a transportation consultant worldwide but is a living encyclopedia of decades of rail-policy drama in our region. He confirmed my worries of lost congressional clout and a tapped-out populace. And the Airport Line, he said, was a heck of a lot cheaper compared with what is being sought for King of Prussia. (The Inquirer archives said that in 1985, it cost $89 million to build. That’s about $210 million in today’s dollars.)

What, then, could possibly make the King of Prussia project move forward?

According to Vuchic, the answer is both quite simple and extraordinarily complicated: “That strongly depends on who controls the U.S. House and Senate. I think elections next year will be drastically important.”

Or, if someone’s got one buried in a drawer out there, a Plan B that doesn’t rely on local taxpayers.

Anything short of either is as far-fetched as a Philly full of blind optimists.