Botanists and biologists have it so much easier than those of us who study the political world.

 

In the life sciences, there is an established nomenclature to determine the phylum, class, order, family, genus and species of plants and animals.

 

Tuesday’s defection of Sen. Arlen Specter (D-PA) from the Republican ranks demonstrates how difficult political taxonomy can be.

 

Less than six weeks ago, Specter told The Hill that he was “staying Republican because I think I have a more important role to play there.” The Senator added that he was “afraid that we’re becoming a one-party system, with Republicans becoming just a regional party.”

 

In botany, it’s simple to classify plants. Is there a stem? What’s the venation of the leaves look like? Does it flower? Visible features offer lots of clues to determine various flora.

 

It’s more puzzling in politics. Particularly when you’re stuck with a comment like Specter’s just a few weeks ago.

 

For years, Senate Democrats tried to court former Sen. Lincoln Chafee (R-RI) to join their side. Sometimes Chafee voted more often with the Democratic leadership than even its moderate, southern senators. Chafee openly supported gay marriage. He was the only GOP senator to vote against the war in Iraq and the League of Conservation Voters and the Sierra Club repeatedly backed him.

 

Rhode Island voters rewarded Chafee for his efforts in 2006 by electing Sen. Sheldon Whitehouse (D-RI) to take his place.

 

Chafee endorsed President Obama last year.

 

At the time, a Republican friend of mine said that it was impossible to determine whether Chafee was a true Republican. She likened it to trying to evict a ghost from a haunted house. “You can never be sure whether (he) was in there in the first place,” she said of Chafee.

 

Former Sen. Zell Miller (D-GA) may have been the polar opposite of Chafee.

 

Miller authored a Constitutional Amendment to bar all same-sex, domestic partnerships. He voted to drill in the Arctic National Wildlife Refuge (ANWR). He supported President Bush for re-election in 2004 and was invited to give a major address at the Republican Convention.

 

In the speech, Miller declared that “no pair has been more wrong, more loudly, more often” than Sen. Ted Kennedy (D-MA) and the 2004 Democratic presidential nominee John Kerry (D-MA).

 

Miller also railed against Kerry’s votes to U.S. weapons systems.

 

“This is the man who wants to be the Commander in Chief of the U.S. Armed Forces?” questioned the Georgia Democrat. “U.S. forces armed with what? Spitballs?”

 

Miller was asked repeatedly why he didn’t just convert to a Republican. He always answered with the same refrain.

“I was just born a Democrat and I guess I’ll just die one,” Miller said.

When it comes to classification, Sen. Joe Lieberman (I-CT) is the duckbilled platypus of the political kingdom. Neither fish nor fowl. A mammal. But with asterisks.

Up for re-election 2006, businessman Ned Lamont upended Lieberman in the Democratic primary. So Lieberman declared himself an “Independent Democrat.’ He declared he was a “loyal Democrat” but still ran as an independent. Lieberman edged out Lamont and the Republican nominee and returned to Washington.

But not without controversy.

Although he was Al Gore’s running mate in 2000, Lieberman endorsed GOP nominee Sen. John McCain (R-AZ) for president and spoke at the 2008 Republican convention.

Democrats mulled either kicking Lieberman out of their caucus or stripping him of his chairmanship of the Governmental Affairs Committee -- or both. But President Obama intervened and persuaded Democrats to allow Lieberman to continue to caucus with them.

Other high-profile lawmakers have enjoyed dalliances with the opposite side. Former Sen. Bob Smith (R-NH) left the GOP so he could run for president as a third-party candidate. When Lincoln Chafee’s father John died, Smith rejoined the GOP so he could chair the Environment and Public Works Committee. Smith said it was “a mistake” to repudiate the GOP and said he never switched his voting registration.

Voters booted Smith in the 2002 GOP primary in favor of former Sen. John Sununu (R-NH).

In the animal kingdom, you might find Pagurus bernhardus, better known to us as a hermit crab. Hermit crabs shuffle from shell to shell, adopting anything from a vacant shell discarded by a sea snail to a conch for their protection.

Depending on the political tides, politicians are known to inhabit various shells as well. That’s because political labels serve as shells. Democrat. Republican. Conservative Liberal. Blue Dog. Fiscal Conservative. Progressive. Socialist. These are all just armor protecting the political animal inside.

Which is why politicians like Arlen Specter make it hard to truly know the genus and species of the creatures that populate the Congressional sandbar.

- Chad Pergram covers Congress for FOX News. He’s won an Edward R. Murrow Award and the Joan Barone Award for his reporting on Capitol Hill.