For a group of TV anchors and reporters, the team at Fox News are keen scribblers. Often with co-writers, former host Bill O’Reilly writes of assassinations and Brian Kilmeade authors histories. Bret Baier is chief political anchor but has also written several books as a “reporter of history”. Now comes a biography of Ulysses S Grant which focuses on the grave constitutional crisis following the disputed election of 1876.

Magnanimous in civil war victory, Grant was elected in 1868 on the theme of “Let us have peace”. By the nation’s centennial eight years later, Americans had wearied of scandals, economic troubles and federal troops in the south, seeking to enforce to some degree the new civil rights of Black Americans, notably the vote. In 1874, Democrats took the House. Now they wanted the presidency.

They nominated the New York governor, Samuel Tilden, a moderate nevertheless supported in the south. The Republicans picked Rutherford Hayes of Ohio. It was a bitter campaign, filled with threats of violence, each side playing to its base.

Tilden performed surprisingly well in the north, winning his home state and four others. Hayes winning Indiana and Connecticut alone would have prevented the subsequent controversy. He did not, but he did win Louisiana, South Carolina and Florida, southern states with Republican governors.

Hayes needed all three states to win. “Self-appointed Democratic counters”, however, submitted results for Tilden. As Grant said: “Everything now depends on a fair count.”

Tensions ran high, with rumors of southern militia marching on Washington and US troops on standby. Baier writes that Grant “had influence, and he decided to use it to expedite a fair result – even if that result required sacrificing his own achievements”.

Grant knew that to be seen to be fair, the result must “appeal to [the people’s] sense of justice”. For that, both parties had to agree – and the south had to support Hayes. At Grant’s insistence, an electoral commission was formed, the deciding vote given to the supreme court justice Joseph Bradley. Bradley chose to support the states’ official electoral certifications. Hayes won. Tilden did not pursue extraordinary means to ensure victory, stopping a bribery effort in his favor.

But the battle was not over. Grant believed Louisiana’s certificate was probably fraudulent, and there was bedlam in Congress. Grant favored compromise and Edward Burke of Louisiana effectively proposed a trade: Hayes for the presidency, Democrats for the disputed governorships of Louisiana and South Carolina.

A separate group of Republicans – acting without Grant – then promised Democrats Hayes would withdraw troops from the south. In return, Democrats would agree that Hayes was duly elected, along with vague and worthless promises to respect Black rights. At this point, Baier writes, “the nation breathed a sigh of relief”.

Baier clearly admires Grant – and there is much to admire. Though betrayed by false friends, as president Grant exercised his office with firmness where necessary and with a passionate desire to inspire Americans towards greater unity. Political inexperience cost him dearly.

But what of the big issue? Did Grant really put an end to Reconstruction and consign Black Americans to nearly a century under Jim Crow?

Hayes had shown a willingness to end Reconstruction. Tilden would certainly have done so. Grant strongly supported Black suffrage and kept troops in the south to ensure the rights of people increasingly threatened by armed violence. He sent troops to an area of South Carolina especially marked by Klan violence and vigorously promoted and enforced an anti-Klan act. He sent troops to Louisiana to enforce voting rights and secured passage of the 1875 Civil Rights Act.

Nonetheless, the supreme court reduced Black rights, and as Baier writes, “the country no longer supported the use of federal troops”. Grant had his army but had lost his people.

He promoted a compromise in 1877 not from any desire to abandon the Black community but from the painful realization that America had tired of the journey. Whether Hayes or Tilden had been elected, Reconstruction was over and a more painful era in the south was about to begin.

The problem wasn’t Grant, but that America was not ready to live up to its promises.

Baier begins and ends his book with the events of 6 January 2021.

“What happens,” he asks, “when the fairness of an election is in doubt, when the freedom of the people is constrained, and when the divisions on the public square strangle the process?

“What can we learn from the healing mission of our 18th president that might show us a path towards union?”

Baier answers the second question only implicitly. He echoes the historical consensus that the “sad and inescapable truth is that there was no way of knowing the right verdict”.

True in 1877. Clearly not in 2021.

After Appomattox, the Confederate general James Longstreet, a friend of Grant, asked “Why do men fight who were born to be brothers?”

The answer frequently involves failures of political leadership. Baier writes that Grant “knew that in times of great national conflict there are only two choices – to stand for division or to stand for peace”.

Grant used his power for good, to promote national unity. Donald Trump did not say the words or take the actions that Grant did during an equally if not more severe challenge to democracy. Baier misses an opportunity for Grant-like firmness in not asking why Trump failed to call on his supporters to accept the result. Rather than simply speaking of America’s strength and resilience, why not point out directly the contrast with a president who stood for division?

In 2021, the national sigh of relief did not come until after noon on inauguration day, as President Biden took the oath.

The danger persists, and not every president is Gen Grant.

• To Rescue the Republic is published in the US by Custom House