She’s supposed to be a 2020 presidential juggernaut, but lately U.S. Sen. Elizabeth Warren’s campaign is stumbling along like a clunker.

Warren blundered her way through what should have been a softball interview with CNBC, raising the possibility she wanted to raise the top tax rate to 50 percent or higher.

“Here’s how I look at budgets and taxes,” Warren lectured. “A lot of people think they’re just numbers, they’re not. They are the expression of our values.”

Oh, pardon the rest of us for stupidly thinking that numbers are important in putting together budgets. All this time I’ve been budgeting for $100 a week in groceries. But now I realize I can spend whatever I want. Those $3 organic avocados are an “expression of my values.”

Warren was pressed on what would be too high for the top personal tax rate, and she once again deferred, saying “It’s not about a number.”

Host John Harwood tried to rescue her asking, “Is 50 percent obviously too high?” But Warren wouldn’t take the hint.

“That’s why you sit down and you negotiate over the numbers,” she said.

Yikes. One more time.

“Do you feel … that it’s wrong for more than half of somebody’s marginal income to be taken?”

Here’s where Warren decided to venture into even more dangerous territory.

“Look, there was a time in a very prosperous America … an America in which working families were doing better generation after generation after generation, where the top marginal rate was well above 50 percent,” she said.

Harwood even tried to bail her out again, saying “It doesn’t strike you as obviously, ‘no, 90 percent, that’s ridiculous.’ ”

“Ninety percent, yes,” Warren replied.

Phew. So if Elizabeth Warren is president, she won’t push for a 90 percent tax rate. How reassuring.

This isn’t the first time Warren veered into super lefty socialist world. Just a few days ago, she claimed on another NBC network that the reason the unemployment rate was so low was because people were working “two, three or four jobs.”

This bit of lefty exaggeration ignores the fact that the rate of people working more than one job has stayed steady in recent years below 5 percent. But Warren is so anxious to peddle her propaganda that she is defying reality.

All this does not bode well for her White House hopes, or even for her hopes of cruising through her re-election race and trouncing her opponent.

Warren has clearly not been challenged very much recently, choosing to hold softball interviews or town halls on friendly turf like Great Barrington and the South End. That’s fine if she wants to settle for a comfortable re-election margin, but not if she wants to emerge as the No. 1 2020 contender.

Warren has to realize that everything she’s saying now will come back to haunt her, including that 50 percent or higher tax rate. Her conservative opposition is ready to pounce, and right now she’s giving them plenty of material.