Tea Party activists have stormed the GOP state assembly, scrutinized candidates at forums across Colorado and regularly protested policies and politicians they dislike since first splashing into the political pool about 15 months ago.

What they haven’t done is deliver more voters to the GOP ranks, which have instead dwindled a bit and left the much-hyped movement’s impact on the general election even less clear.

In the best-case scenario for the Republican Party, GOP leaders say they expect a boost in November turnout and more volunteers in phone banks and on doorsteps.

But the activists’ sway over the GOP primary could make things more challenging for Republicans in November if — as in other states — they succeed in pushing forward candidates with weaker mainstream appeal, analysts say.

The lack of a spike in the number of registered Republicans confirms what many analysts, including Colorado State University political science professor John Straayer, have long suspected.

“The bigger chunk of the Tea Party activists were people who were in the game anyway. They’re just noisier about it,” Straayer said. “They’re going to provide a bit of a boost in terms of getting the vote out.”

A Denver Post analysis of Colorado voter registration in the time frame during which the anti-establishment groups were born and grew in influence — February 2009 to May of 2010 — shows:

• Republicans lost nearly 15,000 active voters — 1.7 percent of their total. The party gained voters during the same stretch in the previous midterm election cycle, secretary of state data show.

• Democrats, coming down off the new-voter high of 2008, lost 39,000, or 4.6 percent.

• The number of unaffiliated voters rose by 20,500, or 2.8 percent.

The three categories remain roughly matched, with each affiliation carrying about a third of Colorado voters.

State Rep. Frank McNulty, R-Highlands Ranch, said the Tea Party activists will vote for and help the candidates with whom they identify.

“This is an important voting bloc that we need to go out and earn each one of their votes,” McNulty said.

Primary turnout hits the roof

In other states where Tea Party candidates enjoyed meteoric victories, falling Republican voter registrations occurred side-by-side with unusually high primary turnouts.

Nevada saw steeper drops in registration numbers than Colorado, but saw greater turnout in the midterm primary election than in the 2008 presidential primary race. Republican voters on June 8 launched previously unknown Sharron Angle toward the November U.S. Senate election.

A slight dip in the GOP ranks in Kentucky — 1.4 percent — mirrors the drop in Colorado. But May 18, Kentucky saw its highest ever turnout at the Republican primary, where Tea Party candidate Rand Paul was nominated for the U.S. Senate race.

Hints of a similar enthusiasm have crept into Colorado politics.

Self-professed Tea Party candidate Ken Buck won the GOP U.S. Senate nomination at the state assembly and leads former Lt. Gov. Jane Norton in some polling.

And Evergreen businessman Dan Maes capitalized on Tea Party appeal to land the top spot on the August primary ballot in the GOP gubernatorial race with former Congressman Scott McInnis.

But no one is sure whether the new and unpredictable faction of Republican voters will turn out with the same force in November if their candidates aren’t chosen in August.

It may be tough to convince a group that hasn’t shied away from lambasting Republicans who they think fall short of conservative standards right along with Democrats, said Lu Busse, chairwoman of a coalition of 25 different 9-12 political groups.

“We hold everybody’s feet to the fire. I do see potential there that some people will be disheartened with certain candidates,” Busse said. “That’s one reason why we’re working so hard to get people involved in the process: It’s harder to have sour-grape feelings.”

Forcing preliminary battles

In the meantime, the largely anti-incumbent activists are forcing primaries to be held in tough races where candidates might not otherwise face an intra-party challenge.

State Rep. Ellen Roberts, R-Durango, was nearly knocked off the ballot when a last-minute Tea Party challenger took two-thirds of the vote at her district assembly in April. She and Dean Boehler are after a highly protected state Senate seat now held by Democrat Sen. Bruce Whitehead.

And in the 3rd Congressional District, Republican state Rep. Scott Tipton tried unsuccessfully to knock Tea Party candidate Bob McConnell out of contention so that Tipton could focus on the difficult task of unseating the Democratic incumbent, Rep. John Salazar.

State Democratic Party Chair Pat Waak looks at the effects of the Tea Party on Republican primaries and sees an opportunity for Democrats.

“The majority of voters are really much more moderate and centrist,” Waak said. “You put forth the most right-wing, off-the-wall candidates and . . . it does help Democrats.”

Jessica Fender: 303-954-1244 or jfender@denverpost.com