Republicans must stick to the Laffer curve.

The Congressional Budget Office just re-estimated its 10-year budget forecast — and lo and behold they’re raising their tax revenue baseline by $1.9 trillion.

This is the same outfit that has been telling us for years that lower tax rates always reduce tax revenues and increase the budget deficit.

But wait a minute: the 2017 Trump tax cuts have been in place for more than seven years.

So is the CBO now suggesting they were wrong all along by admitting that the Laffer Curve really worked? And lower tax rates produced higher tax revenues?

That’s what their new forecast seems to be saying.

In fact, since President Trump’s huge reduction in the corporate tax rate to 21 percent from 35 percent, over the past seven years corporate tax revenues have essentially doubled.

And indeed throw in the lower personal income taxes and other pro-growth measures, the entire federal tax revenue base has gone up about 50 percent.

So how in the world can the CBO come right back and now say that if the Trump tax cuts are simply extended, the 10-year cost is going to be $4 trillion? Cost of what?

There’s no cost.

Keep taxes low and revenues will remain high.

There will be less tax avoidance and better growth.

Mr. Laffer’s been right for about 50 years. The CBO’s been wrong for about 50 years. And here they go again trying to tell us that extending the Trump tax cuts is going to increase the budget deficit by $4 trillion because revenues will be lower.

It is absolute nonsense and Republicans in the House, Senate, and White House should fight the CBO on this.

So far one of the fighters has been Senator Crapo of Idaho — who keeps arguing that if you’re just extending current law, we’re not raising taxes or lowering taxes.

There’s no $4 trillion new deficit.

But if the tax bill is not extended, then you’ll have a $4 trillion tax hike and that will over time make the budget deficit even worse.

Mr. Crapo calls it current policy and hopes the Republicans fight to officially change budget rules.

There is precedent. In 2012 Congress and President Obama extended the George W. Bush tax cuts by using the current policy argument which assumed that the Bush tax cuts would continue — not expire.

Mr. Crapo has said time and again that the CBO doesn’t score permanent spending increases as hiking the deficit every year — and therefore they should not score permanent tax increases.

Otherwise the whole federal fiscal system is like a pinball machine on permanent tilt: always promoting higher taxes, higher spending, and even higher deficits.

Republicans should work hard to reduce unneccessary and counterproductive federal spending.

They should shrink the size and scope of government.

But if they let the tax cuts expire, they’re gonna find themselves with a terrible economy and higher deficits at the same time.

It’s lose lose.

Mr. Trump said we should never get tired of winning. Let’s start by extending the Trump tax cuts and growing the economy by 3 percent or maybe even 4 percent per year.

Call it the blue-collar boom.

From Mr. Kudlow’s broadcast on Fox Business Network.