Pennsylvania's longest-serving U.S. senator has experienced a lot, but Arlen Specter has never before faced voters in a Democratic primary.

Until a year ago, the five-term incumbent navigated political life as a moderate Republican known for his independent streak. He'd defend a woman's right to choose in one breath, and in the next, obtain tax-funded grants for abstinence education in schools.

But last year Specter became one of only three Republicans in Congress to vote for President Obama's $787 billion economic recovery plan. The resulting backlash led Specter to conclude he couldn't win the May 18 Republican primary against conservative Pat Toomey. So Specter switched parties in an attempt at political survival. He has the backing of Democratic Party leaders, but faces a strong challenge from U.S. Rep. Joe Sestak of Delaware County.

So, Democratic voters must decide whether this 80-year-old newcomer to their party is worthy of their support. After all, over the years Specter has cast his share of votes they didn't like; he favored conservative judges and opposed same-sex marriage.

Yet, when you look at the sum of his career and what it has meant to Pennsylvania, you have to conclude he's a good choice for Democrats, which is why The Inquirer endorses ARLEN SPECTER for the Democratic nomination.

Specter has at times disregarded party labels, which made his switch plausible and workable. For years, conservatives referred to him as a RINO - Republican In Name Only. He earned that moniker for his willingness to work across party lines. More than ever, Washington needs lawmakers who are eager to do that.

Specter lost his seniority on Senate committees in the switch, but he hasn't lost his clout. He is still a highly influential lawmaker and appropriator on behalf of Pennsylvanians. He is also one of those rare congressmen who contribute both on the national and international stages. His expertise on the Middle East, federal law enforcement, the judiciary, and health-care research has provided presidents of both parties with valuable counsel.

Sestak, a worthy opponent for the nomination, suffers from low name recognition and the absence of support by party leaders, from President Obama to Gov. Rendell. (He said someone in the White House offered him a job if he would drop out, but has dismissed further questions about that as "just politics.")

The two-term congressman, 58, is a tireless campaigner and has raised an impressive war chest. Sestak says Specter's expertise isn't worth much "if it gives us [Supreme Court Justice Samuel] Alito." He points out that Specter, as a Republican under President George W. Bush, voted for tax cuts that heavily favored the wealthy. Both Specter and Sestak voted for the recent health-care reform law.

A retired rear admiral, Sestak has impressive qualifications. He served as President Bill Clinton's director of defense policy on the National Security Council. After the 9/11 attacks, Sestak became the first director of the Navy's antiterrorism unit. Sestak has been criticized for high staff turnover in his congressional office, but suffice it to say neither candidate is likely to win a Favorite Boss award anytime soon.

A progressive advocacy group has given Sestak a higher rating than Specter, but Specter has been voting more reliably with Democrats since his switch. His recent record suggests that his poor standing with progressives won't last long.

This race is competitive largely due to Sestak's determination and to an anti-incumbent fervor that is bound to hurt the state's longest-serving incumbent. But Specter is a senator for the ages. He is still a vital player and a worthy choice for Democrats.