With everything on the line for his party on Tuesday, Donald Trump has turned into our stuntman in chief.

He has rolled out one phantasmagoric idea after another in recent days, some of them as offensive as they are preposterous.

There is the tax cut of 10 per cent for the middle class that he promised will be “put in” this week by a Congress that is not in session. It was a proposal that no one on Capitol Hill or even his own White House staff had heard about before he blurted it out.

There is his declaration that he will rewrite the Constitution by executive order, revoking birthright citizenship, which no one with any serious understanding of the law believes is within his power.

He has also done something he can do: ordering 5,200 troops to the border, to deal with the supposed national emergency posed by a caravan of destitute migrants. Those asylum seekers are hundreds of miles away and will not arrive for weeks, if they get there at all, given that their numbers are reported to have shrunken by half.

Yesterday morning, the President trumpeted that plan again, tweeting:

“Our military is being mobilised at the Southern Border. Many more troops coming. We will not let these caravans, which are also made up of some very bad thugs and gang members, into the US. Our border is sacred, must come in legally. Turn around!”

It is not the first time Trump has tried a version of this particular stunt.

When Trump sent National Guard troops to the border last spring, something both George W. Bush and Barack Obama had done under similar circumstances, members of the finest military in the world ended up doing things such as feeding the Border Patrol’s horses, shovelling manure from their stalls and fixing flat tyres.

This time, he is taking the unprecedented step of deploying active-duty personnel, in roughly the same numbers as we have serving in Iraq, along with military helicopters and giant spools of razor wire. Trump claims they will be “waiting for” the migrants at the border, implying that US military will be apprehending them as they arrive. But the troops will actually be there in a support role for US Customs and Border Protection, given that the 19th-century Posse Comitatus Act generally prohibits the US military from direct participation in law enforcement. In other words, they will be limited to doing what the Guard was already doing.

The bottom line is this: Trump is using American troops as props, a gesture both wasteful and disrespectful.

We have often heard that Trump’s supporters take him seriously, not literally. But as he spews these ridiculous ideas to stir up his base just before an election, it seems reasonable to wonder: How exactly does he regard them? As gullible, or just indifferent to the truth?

• Karen Tumulty is a Washington Post columnist covering national politics. She joined the Post in 2010 from Time magazine and has also worked at the Los Angeles Times