Washington DC - He didn't mention Donald Trump by name in his State of the Union address, but there was no mistaking President Joe Biden's target as he tore into his predecessor from the outset as an enemy of democracy.

Trump's heavily-promoted live "play-by-play" response to an extended barrage of criticism turned out to be a damp squib – beset by technical gremlins and Trump's odd reluctance to hit back with the same passion.

In his final address before his anticipated November rematch with Trump, the president mentioned "my predecessor" 13 times – dinging the Republican on his anti-NATO statements and campaign of false election fraud claims that inspired the January 6, 2021, assault on the US Capitol.

"My predecessor and some of you here seek to bury the truth about January 6. I will not do that," Biden thundered.

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"This is a moment to speak the truth and to bury the lies. Here's the simple truth: You can't love your country only when you win."

He assailed Trump for encouraging Russian President Vladimir Putin to attack NATO nations that don't meet their financial obligations and the former president's apologism over the invasion of Ukraine in 2022.

Presidents generally avoid giving State of the Union speeches that sound like campaign rallies, but it was clear from the start that Biden was happy to call out his predecessor on all manner of domestic issues too.

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Never one to take criticism on the chin, Trump had promised retorts throughout the speech posted on his social media platform, Truth Social.

But the live commentary ended up being an embarrassing flub as the website crashed before Biden began and stayed out for most of the speech, coming back only intermittently.

The app was spotty too, but Trump was able to get out a few comments on Biden's appearance and demeanor, criticizing his hair and a lipstick mark he spotted on his rival's face, as well as upbraiding the president for coughing.

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"He looks so angry when he's talking, which is a trait of people who know they are 'losing it.' The anger and shouting is not helpful to bringing our Country back together!" Trump posted.

When Trump did turn to policy, he took credit for the country's recovery when Biden brought up the Covid-19 pandemic, slammed Biden over high inflation, and complained about electric cars and his opponent's record on helping veterans.

But he made no direct retort on Biden's most strident criticism, satisfying himself simply with a post crying: "TRUMP DERANGEMENT SYNDROME!"

On immigration, Biden berated Trump's controversial claim that illegal immigrants were "poisoning the blood of our country" and for separating migrant children from their parents, and his ban on entries from Muslim-majority countries.

Trump called an extreme and inhumane Biden-backed bipartisan border bill – blocked by Republicans at Trump's behest – a "disaster," but on the personal attacks, he posted almost nothing.