Democrats and Republicans made an important breakthrough last week when they realized that President Trump will sign any bill they put on his desk.

It was a liberating experience, like discovering your parents have left you and your siblings home alone with the credit cards.

Within hours, lawmakers who normally can’t agree on the time of day had struck a deal to spend hundreds of millions of dollars they don’t have on everything they didn’t get for Christmas.

When Sen. Rand Paul of Kentucky finally went to bed – there’s always one goody-two-shoes who wants to play the grown-up when Mom and Dad are away – his colleagues in both parties tied a bow on the biggest increase in federal spending since the financial collapse of 2008.

The biggest package went to the Pentagon, which will get $719 billion in 2019, up from $634 billion last year. (“We love and need our military and gave them everything – and more!” the president tweeted succinctly.)

Domestic programs got a commensurate 10 percent bump, including a long-postponed renewal of funding for the Children’s Health Insurance Program.

There was even a tax cut – another one, only retroactive this time – to restore $15 billion in tax breaks that expired in 2016 for the year just ended.

One perplexed analyst wondered why Congress would spend billions to incentivize economic activity that has already happened.

Silly party pooper! Why does he think people run for Congress, anyway?

“You get some things you like, you give the other party some things they like,” explained House Speaker Paul Ryan. “That’s what bipartisan compromise is all about.”

There are other kinds of bipartisan compromise, of course – like the kind in which each side gives up something it wants. Or the kind where each side gets something that it wants, but neither side gets everything (“and more!”).

But that’s the kind of big-boy bargain you only have to strike when your parents are home, and sober.

That was not a problem, as it turned out. For all the political calculations that lawmakers were making when they embraced this deal in the wee hours of Friday morning, no one in either party seems to have worried that a responsible adult in the White House would spoil their fun.

And what about the Dreamers – you know, the immigrant children and young adults who Democrats were ready to risk everything for just three weeks ago? It seems, in the race to see how much they could spend before security folks at the credit card company got wise and shut them down, everyone forgot about the Dreamers.

But don’t feel too bad, Democrats! There’s plenty of hypocrisy to go around.

For instance, we know now that the “spending party” is just another name for whichever party has a majority in Congress. This year, it’s the Republicans; next year, who knows?

And don’t cut members of the so-called Freedom Caucus any slack, unless they were as worried about the federal debt two months ago, when Republicans adopted the biggest tax cut most of their top donors had ever seen.

What’s that? You say all those austerity-minded fiscal conservatives voted for the tax cut? (Although in fairness, the grown-ups were away from home that night, too.)

In a just world, the price for all this mischief would fall equally on the unrealistic spendthrifts who went wild and the negligent adults who left them on their own.

But that’s the one respect in which this analogy breaks down, because many of those who will ultimately foot the bill for this bipartisan spending spree haven’t even been born yet. They literally can’t imagine what’s coming.

But the tab will be all-inclusive – everything their parents and grandparents ever dreamed of.

Everything – and more!