Rep. Kenny Hulshof (R-Mo.) announced his candidacy on Tuesday for the newly open Missouri governorship, adding to a growing list of vacant GOP-leaning seats in Congress.

Hulshof’s exit, which has been discussed on and off for six years and drawn a good deal of speculation over that time, could open the door to contested primaries on both sides of the aisle.

Hulshof himself joins a crowded primary that already includes the lieutenant governor and state treasurer. The seat became open when Gov. Matt Blunt (R), the son of House Minority Whip Roy Blunt (R), unexpectedly announced last week that he would not seek reelection.

Hulshof said during a conference call that a conversation with President Bush over the weekend at the House GOP retreat helped seal the deal for him and his family.

“The president said, ‘The best times for my family were the years I was in the governor’s mansion in Texas,’ ” Hulshof said. “That answer assured us … that just because you have the highest office in the state, you can still have some sense of normalcy as a family.”

State Rep. Judy Baker (D) already signed up to oppose Hulshof this year, but former state House Speaker Steve Gaw and state Sen. Wes Shoemyer are both looking at stealing the Democratic nomination with the general election now looking more winnable.

On the Republican side, two candidates rose to the top in the hours after Hulshof’s decision: Rick Steinhoff, the state’s economic development director, and Jason Van Eaton, a longtime aide to Sen. Kit Bond (R-Mo.).

Steinhoff, who is friends with Hulshof, said he is not close to a decision. But he said he is reconsidering everything now that Hulshof is officially out.

It was not the first time Republicans have braced for Hulshof’s exit — not even the first time this cycle. Hulshof looked at running for Senate in 2002 and governor in 2004. Then, last year, he was a candidate for the presidency at the University of Missouri.

“I have had a general interest when any opportunity came up for him, and I’ve looked at his congressional seat, but this is the first time it’s ever become a real possibility,” Steinhoff said.

GOP state Reps. Joe Smith and Bob Onder are also weighing their options. Onder said he will make a decision in the coming days and expects a contested primary.

“The governor’s decision not to run for reelection obviously took everyone by surprise,” Onder said. He later added: “Both sides would wish that there not be a primary, but I think there will be.”

The district favors Republicans and gave President Bush 59 percent of the vote in 2004. But University of Missouri-St. Louis political scientist David Kimball said a competitive race is a distinct possibility.

Kimball said Shoemyer in particular has good cross-party appeal, as would former Lt. Gov. Joe Maxwell, who has also been mentioned as a potential candidate.

“It would still be an uphill battle, but potentially the Democrats could take this seat,” Kimball said. “It’s a Republican seat, but it’s not a hugely Republican seat.”

 The vast majority of the House seats being vacated by Republicans — now numbering 27 — have a moderate degree of Republican advantage built into them.

With very few Democratic-leaning seats currently held by Republicans, these open-seat opportunities are, in many cases, proving better targets than the incumbents that the Democratic Congressional Campaign Committee (DCCC) had initially focused on. Some of them were already targeted before the incumbent announced his or her retirement.

Democrats pointed to the fact that Hulshof’s seat was held by a Democrat for decades before he won it.

“The voters of Missouri’s 9th congressional district have a history of electing Missouri Democrats that share their values,” DCCC spokesman Ryan Rudominer said.

It is also the fourth GOP vacancy created in the last week. Reps. James Walsh (R-N.Y.) and Dave Weldon (R-Fla.) both announced late last week that they would not seek reelection, and Rep. Ron Lewis (R-Ky.) bowed out Tuesday.

Democrats have harped on the mass exodus, while Republicans have expressed confidence in their ability to retain GOP-leaning seats, as they did in a contested special election in Ohio late last year.

“Like we experienced in the Ohio special election, the DCCC has been forced to face the reality that 2006 has come and gone, and that expanding their majority in the House will require more than simply wishing it so,” said Ken Spain, a spokesman for the National Republican Congressional Committee (NRCC).

Hulshof is only the third Republican leaving to run for another office, joining New Mexico Reps. Steve Pearce and Heather Wilson, who are both running for Senate.

The NRCC avoided a similar situation in Missouri, where three GOP members had been weighing the governor’s race.

Rep. Jo Ann Emerson announced Monday that she would not run, and Rep. Sam Graves, who faces the stiffest challenge of any Missouri Republican — from Kansas City Mayor Kay Barnes (D) — also opted for reelection.

Lt. Gov. Peter Kinder and state Treasurer Sarah Steelman are already running for the GOP nomination to replace Matt Blunt. On the Democratic side, Attorney General Jay Nixon has been running and raising money for months, and Secretary of State Robin Carnahan is also thinking about the race.