Several thoughts came to mind when Donald Trump stood in the White House Rose Garden to reveal he was declaring a national emergency over the US-Mexico border.

One was, if there was a genuine emergency – “we have an invasion of drugs, invasion of gangs, invasion of people” – was the president amiss not to have declared this weeks ago in order to keep us safe?

The second, more seriously, was: just how are the Democrats going to handle this?

Not how are they going to deal with this immediate attempt to circumnavigate Congress to get funding for a border wall by inventing a crisis that clearly does not exist, an issue that will most likely be locked up in the courts for months. But how, as it prepares for 2020, is the party going to counter his relentless, scorched earth version of politics, in which he will do anything to win?

Democrats’ immediate reaction was not inspiring. In a joint statement, Nancy Pelosi and Chuck Schumer said: “The president’s actions clearly violate the Congress’s exclusive power of the purse, which our founders enshrined in the constitution.”

Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Show all 20 1 /20 Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters yell as protesters are removed at Trump rally in Texas on February 11 Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen A supporter dressed as a border wall before the rally Reuters Trump Texas rally: Lies, executing babies and attacks on BBC cameramen A man is restrained after assaulting members of the media including a BBC cameraman at the rally AP Trump Texas rally: Lies, executing babies and attacks on BBC cameramen President Trump arrives for a rally in El Paso AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Trump supporters react as a couple are escorted from their seats Reuters Trump Texas rally: Lies, executing babies and attacks on BBC cameramen A supporter shows off a Trump doll while waiting for the rally Reuters Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Linda Padilla Dewiler, originally from Mexico, poses with a sign as Trump supporters gather to attend his rally AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen A supporter sports political badges on his cap Reuters Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters hold signs, one holds an Israel flag, as they cheer for the president AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen President Trump addresses the rally AP Trump Texas rally: Lies, executing babies and attacks on BBC cameramen President Trump addresses the rally in front of a large "FINISH THE WALL" banner AP Trump Texas rally: Lies, executing babies and attacks on BBC cameramen President Trump addresses the rally as supporters hold pro-border wall signs Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen President Trump addresses the rally as supporters hold pro-border wall signs AP Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer at the rally AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer during the rally AP Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer at the rally AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer at the rally AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer the president AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer the president AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters wait for the president to arrive at the rally Getty

Kamala Harris, one of those seeking to take on Trump in two years, said: “We should do something about the actual emergencies that plague our nation – like climate change or healthcare access – not playing politics in order to build a wasteful border wall.”

Alexandria Ocasio-Cortez tweeted: “‘I didn’t need to do this’ means he’s faking a crisis.”

Oh yeah?

And on it went. Journalists on cable news either feigned or expressed genuine shock that Trump had declared a national emergency in a manner no previous president had done.

Somebody suggested it was the kind of issue Bill Weld, a well-mannered 73-year-old businessman who ran as the vice presidential candidate for the Libertarian Party in 2016 and is now considering a primary challenge to Trump, would be able to seize on.

You think?

Anybody who has been watching Trump carefully ought not have been surprised since 3 May 2016, the day he beat Ted Cruz in the Indiana primary and essentially tied up the Republican nomination. On a day when some might have thought to issue words of unity or respect, Trump pointed to a National Enquirer story that claimed Cruz’s father was somehow connected to the assassination of John F Kennedy.

Bill Weld says Trump should read the Constitution

“His father was with Lee Harvey Oswald prior to Oswald’s being, you know, shot. I mean, the whole thing is ridiculous,” Trump told Fox News. Days earlier, he had been retweeting unflattering pictures of Cruz’s wife.

That was the day you knew everything you needed to know about the shameful, but shameless, mentality of the man now occupying the White House. If anyone has been surprised at anything he has done since then, the blame is on them.

With his eye on re-election – and to think there were those who used to imagine Trump would politely stand aside and not seek a second term – Trump has already showed multiple times there is no nihilistic depth to which he will not plunge if it resonates with his base.

From mocking a survivor of sexual assault, as he bulldozed Brett Kavanaugh onto the Supreme Court to placate evangelical Christians, or dragging border agency officials, who were not being paid, into the White House briefing room to declare their support for his government shutdown, he has shown he will do anything – even if it risks bringing down the whole enterprise on him and those around him.

The Democrats need to be ready for a fight that will be as dirty as it gets. They don’t have to try mirror his ugliness, but they need to show they will fight for the things their supporters care about, just as hard as Trump fights for his.

Michael Avenatti, the media-addicted lawyer of Stormy Daniels who himself was once considering a presidential run, summed it up rather well in January, when he referred to Barack Obama’s failure to confirm Eric Garland to the Supreme Court in face of stubborn Republican opposition. “If only my fellow Democrats had fought as half as hard for Judge Garland as Trump is fighting for the wall…”