The dramatic shift in Gov. Charlie Crist’s political fortunes must make him feel like he’s stuck in an episode of “The Twilight Zone.”

When Crist announced his intentions to run for U.S. Senate in May 2009, he appeared to have a virtual lock on the seat.

Despite rancid economic conditions, Crist’s moderate tone and over-tanned charisma produced approval ratings hovering near 70 percent.

On top of that, Crist maintained commanding advantages over his opponent in the Republican primary — former Florida House Speaker Marco Rubio — in every measure of political viability: money, polling and name recognition.

Fast forward to March 2010: Crist is no longer the Sunshine State’s golden boy.

His approval ratings have plummeted to around 50 percent, and he trails Rubio badly in the polls.

Indeed, Rubio has become the darling of the Tea Party movement and national establishment conservatives alike.

He’s been praised effusively in conservative rags like National Review and The Weekly Standard, gave a well-received speech at the Conservative Political Action Conference, and several prominent national Republicans have endorsed him.

Add his steadily climbing fundraising numbers and, all of the sudden, it’s Rubio who is riding the wave of inevitability.

Crist’s desperation was in full view this week when he accused Rubio of using a Florida GOP credit card to get a back wax.

“[Rubio’s] trying to pawn himself off as a fiscal conservative,” Crist said. “And yet just in recent weeks, about two weeks ago, it has come out in news accounts that he had a Republican Party of Florida credit card that he charged $130 haircut, or maybe it was a back wax — we are not sure what all he got at that place.”

To be fair, reports of Rubio’s use of donor money for personal expenses, such as the haircut, repairs on his family vehicle and a stop to a wine store, should give tea partiers pause.

But, then again, this is the crowd that believes President Barack Obama is a Kenyan socialist setting up FEMA reeducation camps. Not exactly a rational bunch.

Still, Crist’s efforts to out-conservative the ultra-conservative Rubio have thus far failed to gain traction.

There are signs Crist may be starting to understand this.

The back-wax kerfuffle notwithstanding, Crist has started to tact back to the center recently.

His proposed budget includes robust increases in education spending — anathema to conservatives.

And when recently given the chance to take a shot at President Obama’s stimulus package, Crist reaffirmed his support of the measure, crediting it with job creation — big time anathema to conservatives.

It almost sounds like he’s gearing up to leave the GOP and run as an independent.

But all that would accomplish is ensure that the Meek shall inherit the senate seat — Rep. Kendrick Meek, that is.

The South Florida Democrat has run an uninspiring campaign so far and trails both of his potential Republican opponents by substantial margins.

If Crist decides to run as an independent, however, he will spilt the Republican vote, almost certainly allowing Meek to win with plurality support.

So what should poor Charlie do?

Easy: join the Democratic Party.

“But won’t voters think I’m a calculating political opportunist if I switch parties?” Crist might ask.

Newsflash, Charlie: You are a calculating political opportunist.

At this point, if you want to continue your political career, your only option is to switch teams.

Crist should take a lesson from Sen. Arlen Specter, a longtime moderate Republican from Pennsylvania.

About the same time Crist started slipping, Specter switched parties.

Specter was in a similar situation to Crist.

Facing an energized insurgent opponent flanking him from the right, Specter read the tealeaves and jumped ship.

At the outset, Specter still seemed unlikely to survive, having admitted that part of his rationale for the switch was his dubious electoral prospects in the GOP primary.

But Specter now finds himself in an excellent position to win re-election. The initial skepticism he endured from rank-and-file Pennsylvania Democrats is dissipating, and he’s now polling competitively against his erstwhile Republican primary opponent.

Crist needs to recognize there is no room for moderates in the modern Republican Party. Dissenting views go unheard amid the din of dogmatic adherence to ideological purity.

The Democratic Party, on the other hand, isn’t called a “big tent party” for nothing.

If the likes of Sens. Joe Lieberman and Ben Nelson are welcome in the Democratic caucus, surely there is plenty of room for Crist.

The electoral calculus is simple, Charlie.

Stay in the GOP and get demolished by Rubio, run as an independent and hand the seat to Meek, or join the Democratic Party and stand a fighting chance.

You’ve got until the April 30 filing deadline to decide. What’s it going to be, Charlie?