“We have God on our side.” They have long been some of the most chilling words in the English language. Perhaps never more so than when uttered by Donald Trump in a re-election campaign.

The president made the claim at an Evangelicals for Trump rally at a megachurch in Miami on Friday night, a day after taking America to the brink of war with the killing in Baghdad of Qassem Suleimani, Iran’s top general and potential future leader.

“He was planning a very major attack,” said Trump, against a backdrop of US flags, “and we got him!” The crowd – many wearing Keep America Great hats, shirts and other regalia – erupted in cheers and whistles.

It was a sure sign of how, impeached and facing a Senate trial as he may be, Trump is already campaigning with a toxic brew of audacity, patriotism and appeals to the almighty. Reflecting on his shock 2016 victory, he told the crowd in Miami: “I really do believe we have God on our side. We’re going to blow away those numbers in 2020.”

For a political outsider who promised to upend Washington, it all sounds remarkably like an old-fashioned Republican pitch. It casts Trump as strongman commander-in-chief, exploiting what the rest of the world has long suspected is an American weakness for jingoism and imperialism. And it seeks to portray his Democratic opponent, whomever it may be, as soft on national security and insufficiently patriotic or Christian.

He was planning a very major attack and we got him! Donald Trump

“As we speak, every Democrat candidate running for president is trying to punish religious believers and silence our churches and our pastors,” Trump claimed spuriously in Miami, eliciting boos. “Well, we can smile because we’re winning by so much.”

Intriguingly, Trump singled out for criticism Pete Buttigieg, a leading Democratic candidate who is both a proud Christian and a military veteran. Buttigieg, the former mayor of South Bend, Indiana, tweeted in return: “God does not belong to a political party.”

Supporters pray as Donald Trump speaks during an Evangelicals for Trump campaign event at the King Jesus international ministry in Miami, Florida, on 3 January. Photograph: Jim Watson/AFP via Getty Images

Meanwhile a Trump campaign video depicts his predecessor, Barack Obama, as if through a dark-tinted lens and with nightmarish music as he talks about the campaign against Islamic State, then bursts into colour as it recounts the killing of its leader, Abu Bakr al-Baghdadi, last year. Trump declares: “You don’t stand a chance against the righteous might of the United States military.”

Faced with this brutally simplistic message, Democratic candidates on Friday asked voters to hold two thoughts at the same time: yes, Suleimani was an enemy of America, but yes, it was also staggeringly reckless of Trump to direct the killing of a government official from another country with little regard for the consequences.

In their view, he is a child playing with matches. The question now is whether Iran will follow through on its promise of “severe revenge” and inflict American casualties, pushing foreign policy up an election agenda so far dominated by healthcare, immigration, taxes, gun control, the climate crisis and the president’s own competence and impeachable conduct.

If America pays in blood and treasure, Trump could be punished at the ballot box, especially as his first campaign was built around promises of “America first” isolation and withdrawing from endless wars in the Middle East.

The strike will definitely help Trump among his supporters. It is the kind of tough talk and action they seem to like Monika McDermott

Monika McDermott, a political science professor at Fordham University in New York, said: “The strike will definitely help Trump among his supporters. It is the kind of tough talk and action they seem to like. Whether it will have any effects outside of that remain to be seen.

“It’s still a long way to go for the general election. The only possible negative I can see from it, in terms of public opinion, is if it opens up a new type of conflict in the Middle East that drags on closer to the election.”

Before then, the killing of Suleimani could shake up the Democratic primary, with the Iowa caucuses only a month away. It offers an opportunity for Joe Biden – whose eight years as vice-president to Obama included the Iran nuclear deal, torn up by Trump – to tout his foreign policy pedigree.

But it also offers anti-interventionist rivals, such as the Vermont senator Bernie Sanders, the chance to attack Biden’s 2002 vote in favour of the Iraq war.

John Zogby, a Democratic pollster, said: “Sanders can certainly take advantage of Biden’s vote on the Iraq war and draw a straight line from there to the destabilisation of the Middle East. Biden can make up for it by saying we negotiated the Iran nuclear deal, they were abiding by the deal and now is this what we want?”

But overall, in the warp speed of the scandal-strewn Trump presidency, it is impossible to know whether Suleimani’s death will loom large or be a half-forgotten footnote come November. Unfortunately for Trump, that outcome may well depend on decisions made in Tehran rather than Washington.

Michael Steele, former chairman of the Republican National Committee, said: “We don’t know how Iran is going to respond to it yet. We don’t know exactly what it may or may not mean domestically here at home.

“How do the American people digest all of this? Because it’s all happening so fast: people woke up this morning and, ‘Oh! We just assassinated the No 2 in Iran.’”