The party of Lincoln is dead. A half century after the civil rights backlash begat Richard Nixon’s southern strategy, Donald Trump announced on Fox News that his accomplishments may have surpassed those of the 16th president.

“So, I think I’ve done more for the black community than any other president, and let’s take a pass on Abraham Lincoln, ’cause he did good, although it’s always questionable.”

Descendants of those freed from slavery under Lincoln? They would probably differ.

Trump grew up in Queens, a New York borough, but his heart belongs to Dixie. He called the Confederate Robert E Lee one of the greatest US generals and said there were good people on both sides in Charlottesville, Virginia, when white supremacists marched in August 2017 and a counter-protester was murdered. Truly, Trump has cast the Republican party in his own image.

Against this bleak backdrop, Edward Achorn delivers The Lincoln Miracle, an in-depth examination of Abraham Lincoln’s successful quest for the Republican presidential nomination at the convention of 1860.

Achorn is Pulitzer finalist, particularly interested in the 19th century and baseball. The Lincoln Miracle is Achorn’s fourth book but second on Lincoln, after Every Drop of Blood, about the second inaugural address of 1864. The Lincoln Miracle is beautifully written, filled with vivid and easily digested prose.

The reader knows Lincoln will prevail, the US will shortly be at war with itself and the Union will triumph at great cost. Foreknowledge does not detract. The Lincoln Miracle’s themes are timeless, its subtitle apt: Inside the Republican Convention that Changed History.

Achorn deftly lays out the personas, demographics and rivalries that shaped the nominating contest and the 1860 election. The Whig party was spent, riven by slavery and nativism. Anti-Catholicism was a force. Anti-German sentiment too. The nation was buffeted by the competing pulls of abolitionism and preservation of the Union. Republicans were divided, Democrats fractured. The Democratic convention was an abject failure. Compromise was not in the air.

Three years earlier, the supreme court had issued its infamous Dred Scott decision, reading slavery into the constitution. Short of constitutional amendment or war, there was little to be done. Slavery had morphed into a right.

At the Illinois Republican convention in 1858, Lincoln delivered what would come to be known as the House Divided speech. “A house divided against itself cannot stand,” he quoted from the Book of Matthew, his Baptist upbringing manifest. Lincoln may have been a deist but he appreciated Scripture. According to Achorn, he believed “pain and failure were endemic to human life”. People could only do so much. The rest was in the hands of an “inscrutable” God.

“I believe this government cannot endure, permanently half-slave and half-free,” Lincoln said. “I do not expect the Union to be dissolved – I do not expect the house to fall – but I do expect it will cease to be divided. It will become all one thing, or all the other.”

Lincoln had served one term in Congress, back in the 1840s. His antipathy to slavery was well known. So was his opposition to popular sovereignty, the notion that new states could decide for themselves if slavery would be legal within their borders. In 1858, Lincoln was running for a US Senate seat. He battled the Democrat Stephen Douglas on that very point. Lincoln won the debates but lost the election. In 1859, John Brown seized the federal armory at Harper’s Ferry, Virginia, in an attempt to arm the enslaved. He was put to death for treason. The glue that held the country together was quickly coming undone.

Lincoln had a rematch with Douglas. In the fall of 1860, in a four-way election, both men vied for the White House. Lincoln had been an underdog for the Republican nomination, never mind the presidency. How he won the first prize before he won the second is a tale worth telling. His political march signaled how he would govern, how he would impose his vision and will on the country.

Lincoln respected the foundational documents, wedding his opposition to slavery to the founders’ stated ideals.

“He was acceptable,” writes Achorn, “because he celebrated the founding fathers and Declaration of Independence. Lincoln believed intensely that the founders had opposed slavery as an obvious contradiction of the values enshrined in the Declaration of Independence and had set it on the road to extinction.”

Nowadays, the 1619 Project takes a different view. The issue is live once more.

Lincoln knew patience could be a virtue, that he could bend time to his side. At the Republican convention, in a huge wooden “wigwam” in Chicago, he was the darkest of dark horses. With each round of balloting, his odds improved. After the first round, Lincoln was more than 70 votes behind William Seward, the New York senator and favorite to be the nominee. After the second ballot, Seward’s margin collapsed. Lincoln’s victory, in the third round, was inevitable. Seward became Lincoln’s secretary of state.

The Lincoln Miracle describes political battles on a stage long vanished. The book lands in an America transformed. The last president from Lincoln’s party demands the constitution be terminated. He considers a return to the White House – and dines with an anti-Semite and a white supremacist.

But 19th-century dynamics have not completely vanished. On the right, John C Calhoun, father of the filibuster, proponent of white supremacy and secession, is praised. Into the Republican presidential race strides Nikki Haley, a Trump appointee turned rival who once told the Sons of Confederate Veterans states had the right to secede. There’s more. The civil war the Confederacy fought to maintain slavery? A matter, in Haley’s weasel words, of “tradition versus change”.

More than 150 years after Lincoln’s assassination, the embers of civil war still glow. The Lincoln Miracle is relevant reading indeed.

• The Lincoln Miracle: Inside the Republican Convention that Changed History is published in the US by Grove Atlantic