Anyone reading this will have already heard Arlen Specter, Senator-PA, has announced a change in party affiliation, changing the 'R' after his name to a 'D'. While many Democrats are excited over this, I find myself with some mixed feelings.
The underlying assumption seems to be the switch, combined with Al Franken eventually being seated, will give Democrats the much vaunted 60th-seat, thus bringing an end to filibusters, and thereby ushering in a new era of peace and prosperity, a cure for cancer and aging, unlimited sources of clean energy and so on.
Reality says otherwise. No matter how much the Republican party may have "left" him by continuing to move to the right, Specter will unquestionably be one of the most conservative members of the Democratic caucus. He's already said he won't be an "automatic" 60th vote, and there is no reason to doubt his word on the matter. It's likely Dems will see Specter vote somewhat more often for cloture than he would have if he had remained in the Republican caucus, but how much more often remains to be seen.
If anything, Specter might be in a similar position to Ben Nelson of Nebraska, where he use the threat of withholding his vote to get changes to various bills he might want, but which don't really mesh with a progressive agenda.
On the other hand, it's quite likely Dems could do better if they were simply patient - Specter was motivated to switch affiliation because it became increasingly apparent he would not win a 2010 Republican primary against Pat Toomey. In the 2004 primary Specter narrowly edged Toomey, the definition of a hard-core conservative, but since then many of the voters who helped him squeak by have re-registered as Democrats. However, if Toomey does, indeed, win the Republican nomination, any Dem with a pulse would defeat him in the general ... so why not wait and get a candidate more in line with the full agenda?
In the near term, I suspect the ultimate effect of the swap will be minimal, other than further emphasizing (if any further emphasis was needed) how truly extreme the core of the Republican party has become. Any larger might have to wait until after the 2010 elections - if that vote were held now, Dems would be favored to collect 3-5 more Senate seats in addition to Specter's (which was already among those most likely to switch parties), which truly would give Democrats a filibuster-proof majority, and would consign Republicans to even greater irrelevance.