Trump has a secret weapon. It's called the Democratic Party.

SAN DIEGO -- The Democratic Party is the gang that can't shoot straight.

The front-runners for the presidential nomination -- Joe Biden, Bernie Sanders, Pete Buttigieg and Elizabeth Warren -- are all defective in some way. In fact, they are all defective in the same way.

The defect fits a pattern of arrogance mixed with incompetence.

First, Democrats lose the 2016 presidential election because their nominee -- Hillary Clinton -- couldn't find her way to Rust Belt states like Michigan or Wisconsin. Having become the party of coastal elites, Democrats promised to roll up their sleeves and devise an economic plan for the working class. That never happened.

Next, Democrats spent three years pushing the narrative that the only reason Clinton lost to Donald Trump was because the Republican colluded with the Russians. This would be the same Clinton who, while serving as secretary of state, made a show of presenting Russian Foreign Minister Sergey Lavrov with a red "reset" button in March 2009 in Geneva, Switzerland. The point is, both parties have cozied up to Moscow.

Then, House Democrats impeached Trump for allegedly offering the Ukrainian government a quid pro quo in July 2019 if it would investigate Biden and his son. In the process, a story emerged about what happened a few years earlier when Biden said he would withhold aid from Ukraine unless it fired a certain prosecutor. Hecklers are calling out "quid pro Joe" at Biden rallies, and the former vice president has slipped in the polls in Iowa and New Hampshire.

Also, by not completing the process and sending the articles of impeachment to the Senate, House Speaker Nancy Pelosi advances the notion that the whole circus was nothing more than an election-year stunt to depict Trump as morally deficient and unfit to serve as president. Clinton used that strategy in 2016. Rather than make the case for why she was the right person to be elected president, she spent most of her time arguing that Trump was the wrong person. How did that work out?

In the Democratic primary, the front-runners are all broken because they're cravenly inconsistent. The person they are in December doesn't match who they pretend to be in January. Who knows who they will be in February?

Warren became part of the top 1% by helping wealthy corporations make more money as a lawyer and consultant, and now she rails against the wealthy and targets Buttigieg for courting rich donors.

Nowhere are Democrats' inconsistencies clearer than with the sticky issue of immigration.

Buttigieg declared his support for giving health insurance to illegal immigrants during the first Democratic debate in June. But a few months later, the mayor of South Bend, Indiana, raised eyebrows among Mexican Americans when he said that he would send U.S. troops to Mexico to combat drug cartels "if American lives were on the line and if it was necessary to meet treaty obligations." The last time U.S. troops marched into Mexico, back in the mid-1800s, our neighbor lost half of its territory in a land grab. There was a treaty then, too, whose provisions the United States largely ignored.

Sanders has spent much of his career pandering to working-class whites who think they lose jobs to immigrants. In 2007, he told CNN's Lou Dobbs that he opposed the landmark bipartisan immigration bill proposed by Sens. Ted Kennedy and John McCain because it included "amnesty" for the undocumented. Now, during a recent visit to San Diego, Sanders promised to give legal status to recipients of Deferred Action for Childhood Arrivals (DACA) and introduce a bipartisan immigration reform bill -- one that will probably resemble the one he helped kill a dozen years ago.

And Biden started out defending President Obama's high number of deportations and telling activists who brought it up to "vote for Trump." Recently, he has adopted a kinder and gentler take on immigration. Biden has acknowledged that the Obama approach was too harsh, especially in breaking up families. His campaign said in a statement that the candidate "understands the pain felt by every family across the U.S. that has had a loved one removed from the country, including under the Obama-Biden administration." He promises a humane version of immigration enforcement.

These quick-change artists seem to be driven by political expediency. The most important quality of a president is character. The Democratic front-runners don't appear to have much of it.

To beat Trump, Democrats must be at the top of their game. Yet, oftentimes, they can't get out of their own way.

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Ruben Navarrette's email address is ruben@rubennavarrette.com. His daily podcast, "Navarrette Nation," is available through every podcast app.