The tactic of Republicans attacking the military records of Democratic presidential candidates dates back to Andrew Jackson's campaign of 1828. The "coffin broadsides" were flyers printed by John Binns and others in an attempt to discredit Jackson by accusing him of "murdering" six militiamen in 1815. You can view one of the handbills here.
Jackson confirmed the verdict of a court-martial that convicted and sentenced the men to death for desertion. In 1828, supporters of John Quincy Adams published handbills, known at the time as "broadsides" which asserted the six men executed were indeed innocent. The handbills challenged Jackson's morality and ethics. Most of the handbills printed prominently featured six drawings of coffins, so they became known as the "Coffin Broadsides."
(a brief history of the battle follows)
A three-month campaign by the British Army and the Royal Navy along the US Gulf Coast concluded with a pitched battle between American forces commanded by then-Maj. Gen Andrew Jackson and Maj. Gen. Sir Edward Pakenham south of New Orleans on January 8, 1815. Because of that battle, the campaign accusations didn't stick, though, because Jackson's defense of New Orleans trumped any charges his opponents could craft.
The British campaign started in Florida. The Spanish in Pensacola purported to be neutral, but still allowed the British to land and occupy their forts. British forces moved from Pensacola to Mobile in September of 1814, but found it already occupied by Jackson. Jackson's troops vigorously defended Mobile, forcing the British back to Pensacola. On 11-November, Jackson received word from New Orleans that intelligence gained from Jean Lafitte indicated that city would be the next British target. He arrived in New Orleans on 2-December and began to organize the city's defense. Unable to move up the Mississippi by the Americans in Fort St. Philip at the mouth of the river, the British entered Lake Borgne, to the east of the city. They proceeded to march from their landing sites on the western shore of Lake Borgne inland to the Mississippi, which put them in modern-day St. Bernard Parish.
By 23-December, the British began to move upriver, occupying the Jumonville and Villerie Plantations. Patrols probed into the LaRonde plantation and found it defended by Jackson, two regiments of US Army soldiers, the Louisiana Militia, and a hodgepodge of local units from New Orleans. The British pulled back to the Villere plantation at this point, awaiting the arrival of a new commander-in-chief, Maj. General Sir Edward Pakenham, GCB. Pakenham was appointed C-in-C of British forces in America after the death of General Robert Ross in Baltimore in September of 1814.
Pakenham's plan was to assault the positions along the Rodriguez Canal on the LaRonde Plantation. Jackson's forces fortified the mile-and-a-half of the canal that ran from the river to swamps just north of the plantation. Pakenham ordered a very typical, Continental-style seige attack, with one column advancing along the river road and a line of infantry advancing to the center and right.
A lot has been made of the role of the "Caintock (Kentucky)" riflemen positioned along the ramparts. Kids are taught that these riflemen are responsible for killing thousands of British troops on 8-January-1815. This isn't quite accurate. Pakenham's assault was based on the assumption that casualties would be high. His seige troops were to bring ladders with them, to be placed over the ramparts so the succeeding troops would cross them and overwhelm the defenders.
The 44th Regiment of Foot was tasked with bringing the ladders, but they failed to advance with them. Thus, they and the 93rd Foot (Sutherland Highlanders) were unable to cross the canal and ramparts. In fact, no British troops crossed the Rodriguez Canal save as prisoners of war.
While leading the second wave of the British advance, Pakenham's horse was shot from underneath him. While mounting a second horse, he was struck twice and killed instantly. Unable to breach the ramparts, the British withdrew from the field.
New Orleanians still give thanks to Our Lady of Prompt Succor for the deliverance of the city from the British, even though Jackson was a Protestant.
Maps are from Lossing's Field Book of the War of 1812.