A good illustration of this is that, he was once a Democrat who became a Republican who has now become a Democrat. Even though this is considered to be a somewhat rare occurrence. He is actually the 13th Senator to become a switch hitter since 1913.
Some say he caught the public's eye when he ran for Mayor of Philadelphia in 1967. However there are many more who believe that he caught the eye of the powers that be when he pulled the Warren Commission's chestnuts out of the fire, following the John F Kennedy assassination back in 1963.
Then, a lowly attorney in Philadelphia, his services were recommended by Representative Gerald R. Ford and he became the Assistant Council for the hastily created Commission. His duties included investigating and prosecuting the case against Lee Harvey Oswald who was accused of being the "-lone gunman' at the time.
Arlen took to his duties with the relish of true opportunist. Always the aggressive prosecutor, he was like a bulldog in a meat market. Threatening, harassing, intimidating and bullying almost all of the eye witnesses who were allowed to testify before the Commission. Selectively channeling all of the forced testimony and questionable evidence to the already forgone conclusion of Oswald's guilt.
Just the fact that Arlen was able to use this "tall tale"- to convince a committee consisting of two prominent US Senators, one Republican one Democratic; two prominent House Members one Republican one Democratic; two prominent spy masters (one that JFK just recently fired) and the Chief Justice of the United States Supreme Court seems to commend his oratory skills. However, when you consider that these appointees of the (accidental) President Lyndon B Johnson were in fact all conservatives and, to a man, were not quite enamored with our slain President nor the direction that JFK was charting for Americas' future. Arlen's skills may have been slightly overstated.
Railroading the "-lone gunman' was necessary. So selling this "tall tale"- was critical to all concerned. Without it, one would be forced to assume that there was more than one assassin that day in Dallas. Which, by logical conclusion, would mean that there was (my gosh!) a conspiracy. Considering that 1) both LBJ and J Edgar Hoover had already stated that Oswald was the LONE assassin and, 2) that Lee Oswald had also been conveniently eliminated (so there would be no trial). It was generally accepted that Arlen's efforts encouraged everyone to jump onboard the train.
In 1976, Specter ran in the Republican primary for the U.S. Senate and was defeated. He was also defeated when he ran in the Republican primary for the Governor of Pennsylvania in 1978. However, when he ran again for the U.S. Senate in 1980, he was finally victorious. As he became the junior Senator from Pennsylvania his contradictive tendencies continued. To the consternation of supporters and detractors alike.
Even though his opposition to Supreme Court nominee Robert Bork did not endear him to his fellow Republicans his antagonistic interrogation of Anita Hill during the Clarence Thomas hearings was considered by some Democrats as being vaguely reminiscent of the Spanish Inquisition. Although, at one point he actually accused her of "flat out perjury."- In the end he didn't put a "-contempt of Congress" charge where his mouth was.
While primarily continuing to tow the party line he was also vocally critical of fellow Republicans for their impeachment of President Bill Clinton. Even though he is recorded in Senate records as giving a "not guilty"- vote. In actuality, he cited Scots law to render a verdict of "not proven."
Throughout the years you could always be sure that Arlen would be loyal to Arlen. While he outwardly appeared to be an opponent of President Bush's warrentless wiretapping of US citizens, he ended up voting for the Foreign Intelligence Surveillance Act Amendments in 2008--effectively placing the executive branch almost exclusively in charge of federal electronic searches.
Arlen's defection to the Democratic Party is in reality due in part to ongoing polls taken by Quinnipiac University, which have illustrated that Specter has a higher approval rating among Democrats in Pennsylvania than Republicans, 62-55 respectively--that plus the sobering fact that he is being targeted by rightwing conservative PACs. These influential money sources are bankrolling far less moderate opponents for the upcoming Republican primaries. Being, as always the, "-fair weather friend' Arlen decided to change horses in midterm.
His ex-fellow Republicans have certainly not bade him well, as they were all standing (like Brutus and his chums) with sharpened knives, hidden behind their backs. If I may geo-historically mix a metaphor, Arlen Specter is kind of like the Trojan Horse. You can see what he is on the outside but you never know which Arlen awaits you on the inside. He's a man (it seems) whose principals flow any way the wind blows.