Missouri voters dumped embattled Gov. Bob Holden in favor of state Auditor Claire McCaskill in the Democratic primary yesterday, delivering Holden a stunning defeat after a term that has been mired in turmoil since his first day in office.

Holden is the first sitting governor in a decade to lose a primary.

With 94 percent of precincts reporting, McCaskill had 414,388 votes, or 52 percent, compared with Holden's 363,282 votes, or 45 percent.

McCaskill, 51, will face GOP Secretary of State Matt Blunt in November in a race that could have broad political implications. Experts say the gubernatorial candidates could help carry either President Bush or Sen. John F. Kerry (D-Mass.) to victory in this key swing state.

The gubernatorial race was part of a full ballot that also included a constitutional amendment to ban gay marriage and a primary to fill the seat of retiring Rep. Richard A. Gephardt. State Rep. Russ Carnahan, scion of a prominent Missouri political family, was seen as the favorite to win the Democratic primary and prevail in November in Gephardt's district, but he was locked in a tight, four-way battle for the nomination. The gay marriage ban was approved overwhelmingly. It was the first such vote since the historic ruling in Massachusetts last year that legalized same-sex weddings there.

A constitutional amendment to build a casino near the country music resort town of Branson was defeated.

Republican Sens. Christopher S. Bond of Missouri and Sam Brownback of Kansas defeated little-known opponents to win their respective nominations.

In Michigan, former state senator John Schwarz won a six-way Republican primary in the race to replace retiring Rep. Nick Smith (R). Schwarz lost to Smith 12 years ago. The race also included Smith's son, Brad Smith.

In Chicago, Republican leaders narrowed their search for a new Senate candidate to former presidential hopeful Alan Keyes and former Bush administration deputy drug czar Andrea Grubb Barthwell. One will be chosen today to take on heavily favored Democrat Barack Obama.

Jack Ryan, the Republican primary winner, dropped his Senate campaign in late June over embarrassing allegations about his sex life.