RUBEN NAVARRETTE JR.: Biden a strong warrior for some supporters. For others, not so much.

With just a day to go before the first presidential debate, the stakes could not be any higher for President Joe Biden.

Even in a rematch with an opponent who divided the country and left the presidency in shambles — and who was convicted of 34 counts of falsifying business records to cover up hush money payments intended to interfere with the 2016 election — Biden can’t get traction.

I have a theory: Biden can be his own worst enemy.

The president has lost support from three groups that need to show up for him in November: Latinos, Blacks and young people.

Many of those voters — who backed him in 2020 — are disappointed and disillusioned by Biden’s policies, priorities and performance. So they’re reluctant to vote for him again.

I’ve heard from members of all three groups. And what I hear fits with news reports that examine Biden’s lack of support with these voters.

Many Latinos think that Biden was timid and weak in pushing immigration reform and that he was too eager to adopt Trump’s enforcement policies, such as eliminating asylum and building a border wall.

Even Biden’s recent executive action to “parole-in-place” undocumented immigrants who are spouses of U.S. citizens — a change that could impact as many as 500,000 people — may not be enough to convince Latinos that he is in their corner.

Some Black Americans believe that Biden didn’t do enough to support voting rights legislation named after Democratic Rep. John Lewis, the late civil rights champion; narrowly passed by the House, the bill has languished in the Democratic-controlled Senate since 2021. Other Black voters are angry at Biden for not keeping his promise and doing more to reform policing after the killing of George Floyd by a Minneapolis police officer.

As for young people, polls show that many in this cohort strongly oppose Biden’s support for Israel and remain critical of the administration’s inability to bring about a cease-fire in Gaza. The protests on college campuses this spring made it clear that those who oppose Israel’s war against Hamas terrorists hold Biden responsible for much of the death and destruction happening in the Middle East. And they’re likely to remember in November.

Biden’s critics can point to other instances where he has shown the very things that they want him to show in dealing with the issues they care about: strength, courage and resolve. When it comes to protecting women’s reproductive rights, supporting labor unions or pushing to eliminate student loan debt — even when it means defying the Supreme Court, Biden is all in. He is ready to fight to the bitter end.

That must make his critics even more furious. If he can summon the will to do the hard things when it comes to fighting for some causes, why can’t he do that with others?

It’s not just about the level of resistance that he might encounter from Republicans. The abortion debate is every bit as contentious and divisive as the immigration debate, and yet Biden doesn’t budge or negotiate or equivocate when it comes to supporting a woman’s right to choose. Likewise, Republicans still oppose Biden’s plan to forgive student loan debt for hundreds of thousands of borrowers, but he doesn’t seem to care.

Republicans like to say that Biden is weak and indecisive, and the polls show that a majority of voters agree with that assessment. But it’s more accurate to say that Biden is weak and indecisive only some of the time, on issues where he finds the politics to be especially complicated — such as immigration, police reform or the Middle East.

Naturally, the worry about whether Biden is strong enough to be an effective president are compounded by persistent concerns over his age. According to an ABC News/Ipsos poll in April, more than half of Americans say both Trump (at 78) and Biden (at 81) are too old to serve another term. Although it’s also true that polls also show that voters are more concerned about Biden’s age and mental acuity than they are Trump’s.

For all these reasons and more, Biden needs to win the debate with Trump. But to win the presidency, he’ll need to show his supporters that he doesn’t play favorites with what promises he keeps, and which causes he decides to champion.

If he is going to suit up for one battle, then he needs to suit up for them all.

Ruben Navarrette’s email address is crimscribe@icloud.com. His podcast, “Ruben in the Center,” is available through every podcast app.