Ordinarily, the resignation of a state senator -- particularly one not tinged with scandal -- is of no more than passing interest. In fact, two senators already had resigned early this year to take their seats in Congress.

However, when Sen. Michael Rubio, D-Bakersfield, unexpectedly announced Friday that he was leaving the Senate to become a governmental affairs executive for Chevron Corp., it created a political stir.

There is no reason to believe that there is anything behind his departure other than what he said it was -- a chance to spend more time with his family, including a daughter with Down syndrome -- and presumably a chance to earn more income for that family.

His resignation created a stir because he was a rising political star with a fair chance of becoming president pro tem of the Senate, and a key member of the Senate's informal bloc of moderate Democrats who will determine the new supermajority's impact on legislative policy.

In that mode, Rubio had been the chief champion of altering the iconic California Environmental Quality Act, a reform that Gov. Jerry Brown and Democratic leaders say they support and that environmental groups are reluctant to do.

Rubio's resignation was so sudden that it surprised a CEQA reform coalition just as it was announcing draft CEQA legislation.

The current Senate president pro tem, Darrell Steinberg, went ahead and introduced the draft, but Rubio's departure alters CEQA reform dynamics to some degree.

It also changes the arithmetic of the Senate, at least temporarily. With three Senate seats vacant, and a fourth vacancy likely later this spring if and when Sen. Curren Price becomes a Los Angeles city councilman, the Democratic supermajority of 29 seats won't be fully operational until late in the legislative session. And as Assembly members move up to the Senate in special elections, the Assembly's supermajority also temporarily shrinks.

Liberal groups want the supermajorities to forge ahead with legislation that they can enact without Republican votes, including, perhaps, tax increases.

However, moderates such as Rubio -- perhaps a half-dozen senators in all -- determine how far the Senate's supermajority will go down that path, so the special election to fill his seat takes on added importance.

Finally, Rubio's resignation would appear, at last superficially, to clear the pathway for Sen. Kevin de Leon, D-Los Angeles, to become Steinberg's successor. It's uncertain, however, with the next speaker of the Assembly likely to come from Los Angeles, whether having a Senate leader from the same city would be tolerable to Northern California's interest groups.

There has been an informal understanding in recent years that the Assembly speaker comes from Los Angeles while the Senate leader comes from Northern California.