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By Kurt Bardella

The one-time home of the “Reagan Revolution” is now essentially a third party in California.

New data released at the end of May shows the California Republican Party lagging behind both the Democratic Party and independent voters in voter registration. Democrats make up 44.6 percent (8.4 million) of the electorate while 25.5 percent (4.8 million) are comprised of no-party preference voters. The Republican Party is down to 25.5 percent of the state’s voters (4.7 million), roughly 73,000 fewer voters than the total of self-described independents.

And so as Californians of all political affiliations head to the polls Tuesday for the 2018 primary elections, strategists around the country will be watching closely. And unless something dramatic happens, the California GOP’s relegation should serve as a clear warning to national conservatives who embrace a radical policy agenda.

Ignoring contemporary, mainstream American values is simply not a winning strategy for the GOP.

Simply put, the Republican Party in California seems to be heading towards political irrelevance. Not a single Republican serves in any of the statewide offices. California Democrats already have a supermajority in the Senate and are just one seat short of a supermajority in the Assembly.

Make no mistake about it, this is where following Donald Trump will ultimately lead; ignoring contemporary, mainstream American values is simply not a winning strategy for the GOP.

Not that this is much of a surprise. For the better part of the last 25 years, Republicans in California have systemically eroded their reputation as the so-called "big tent" party by cowardly catering to the extreme fringe while ignoring the demographic realities of an evolving population.

Consider a new Lane Center poll that found that less than a third of Californians supported a border wall. That same poll also found strong support (66 percent) for making 21 the minimum age for gun ownership; 59 percent of respondents supported a ban on assault weapons. Polls also show that almost half of Republicans now say the laws covering gun sales should be stricter, up from 28 percent a year ago. The Public Policy Institute of California (PPIC) found that four in five Californians say global warming is a serious threat to the state’s future.

For the better part of the last 25 years, Republicans in California have systemically eroded their reputation as the so-called "big tent" party by cowardly catering to the extreme fringe.

Now look at those same issues from a national lens.

According to Gallup, two-thirds of Americans support tougher gun laws. A CBS News poll found that 60 percent of Americans oppose building a border wall. A new report published by Pew Research found that most Americans believe that the federal government is doing too little to protect the environment and reduce the effects of climate change.

The Republican Party is completely out of step with national attitudes on major public policy and societal benchmarks. This has become increasingly evident recently in California, where the GOP’s fixation with pleasing the base has come at the expense of expanding its to the next generation of potential voters: young people, minorities and women.

In 1994, Gov. Pete Wilson led the crusade for Proposition 187, a measure to prohibit undocumented immigrants from access to state services like education and healthcare. Pop. 187 permanently cast the GOP as anti-immigrant and was an important step in the process of turning California blue. Current Republican gubernatorial candidate John Cox, Trump’s choice in the race, once warned that gay rights could “open the floodgates to polygamy and bestiality.” And when Republican assemblyman Chad Mayes bucked his party to support climate change legislation, his outraged peers led a campaign that resulted in him resigning from his leadership post.

Californians today believe in climate change, women's right to choose, gay marriage, legalization of marijuana, common-sense gun reform and comprehensive immigration reform. Republican candidates running on anti-gay, anti-immigrant and anti-science platforms are out of touch with reality.

California gubernatorial candidate John Cox speaks during the California Republican Party convention in San Diego on May 5, 2018.Gregory Bull / AP

This same denial seems to be afflicting conservatives when it comes to demographics as well. In California, minorities have become the majority. Three years ago, Latinos officially outnumbered white residents. At the national level, new census projections forecast the nation becoming “minority white” in 2045.

Just like in California, the Republican Party is running out of white voters. It’s almost a self-fulfilling prophecy at this point. As conservatives chant “build the wall” to appease a block of voters that is dying off, they are alienating themselves from the group of voters that will outlive and outlast them.

Unless the Republican Party adapts to the demographic reality of America, it is destined to follow the California GOP’s fate and become an irrelevant third party. After all, as goes California, so goes the nation.

Kurt Bardella is an NBC News THINK contributor. He is a former spokesman for the chairman of the House Oversight and Government Reform Committee, Rep. Darrell Issa, R-Calif., as well as for former Sen. Olympia Snowe, R-Maine, and former Rep. Brian Bilbray, R-Calif. Follow him on Twitter: @kurtbardella.