Last week, Ted Cruz, the unexpectedly endangered Republican senator from Texas, warned that Beto O’Rourke, his Democratic opponent, would turn the state into California, with “tofu and silicone and dyed hair.” Does Cruz really think every blonde in Texas — and every middle-age man with remarkably little gray — is natural, and nobody has had work done?

Meanwhile, Sen. Joe Manchin, D-W.Va. — which went for Donald Trump by 40 points — seems to have the edge in his re-election campaign. His secret weapon? Defense of the Affordable Care Act, which drastically reduced the number of uninsured residents in his state.

These two races epitomize how the 2018 campaign is playing out. On one side, Republicans are running almost entirely on identity politics — white identity politics — rather than policy. True, they’re running a lot of ads about immigration, but not about immigration’s actual effects. Instead, they’re all about a mythical wave of crimes committed by scary dark people.

On the other side, Democrats are running on policy issues, above all health care.

But politicians make lots of promises, which are often empty. Are Democrats really credible on health care?

Almost five years after Obamacare went into full effect, the answer is a very clear yes. It hasn’t worked perfectly, and its successes haven’t come in quite the form its proponents expected. But it has delivered huge progress, especially in states run by politicians who are trying to make it work.

It’s worth remembering what Republicans said would happen before the ACA went online: that it would fail to reduce the number of uninsured, that it would blow a giant hole in the budget, that it would lead to a “death spiral” of rising premiums and declining enrollment.

What actually happened was a dramatic fall in the uninsured, especially in those states that expanded Medicaid. The budget costs of expanding Medicaid and subsidizing other insurance have been significant, but estimates for 2019 suggest that these costs will be around $115 billion — much less than half the revenue lost due to the Trump tax cut.

What about that death spiral? Premiums on the health exchanges established by the ACA initially came in much lower than expected, then rose sharply when the people signing up for those exchanges turned out to be fewer and sicker than insurers had hoped. But the markets have now stabilized, with only modest premium increases for 2019 and insurers returning to the exchanges.

What’s particularly impressive about Obamacare’s stabilization is that it’s happening despite desperate attempts by Trump and his allies to sabotage his predecessor’s achievement.

Of course, Obamacare would be doing even better if it were run by people who weren’t trying to kill it. Look at what’s happening in New Jersey, where a Democratic governor and Legislature have used their powers to undo most of the Trumpian sabotage: 2019 premiums will actually drop 9.3 percent, even as they rise modestly in the nation as a whole.

Now, Obamacare is hardly a perfect system. It was always an awkward compromise reflecting the political constraints of the time.

But the Affordable Care Act really did achieve a lot. And this achievement bears strongly on the current political debate. Basically, Democrats have earned a lot of credibility on health care: They delivered what they promised, and they have showed that they can build systems that work.

So are Democrats justified in running as the defenders of American health care? Yes.