From his earliest days in the army during the Revolutionary War, Wilkinson used his position as an aide to generals (Gates, Greene, Arnold) to curry favor, but made a habit of turning on his patrons as soon as it suited him. After getting caught out in this during the Conway Cabal fiasco Wilkinson found his future prospects for command and advancement in the Continental Army looking bleak, so he slunk away. A sly political operator, though, Wilkinson worked his contacts and got himself appointed clothier general, a position at which he proved uninterested and ineffective. This led George Washington to repeatedly call for his ouster, which was finally accomplished in 1781 (when Congress voted to cut his salary in half, prompting Wilkinson to resign).
Decamping to the Kentucky frontier, Wilkinson became involved in an effort first to create an independent Kentucky government, and then with attempts to open the Mississippi River to trade by negotiating with the Spanish in New Orleans. Courting the Spanish imperial authorities with promises, Wilkinson in effect pledged to bring Kentucky into the orbit of Spain in exchange for trading rights, and arranged to receive payments from the Spanish in return for information and efforts on Spain's behalf in Kentucky (this became known as the Spanish Conspiracy). By December 1792, Linklater writes, Wilkinson was undoubtedly committing treason (he was drawing payments from Spain and providing them with vital information, while at the same time commanding an American army regiment).
Linklater carefully documents the ways in which Wilkinson managed to undercut his personal, political and military foes, while flattering and courting those who could advance his career (most notably a whole string of secretaries of war and presidents from Washington to Jefferson). Notwithstanding a body of evidence and rumors regarding Wilkinson's treason (it was remarkably well known), those in power continued to reward him with duties, positions, and responsibilities. Jefferson in particular was surprisingly indulgent of Wilkinson, particularly after Wilkinson opted to betray Burr's plans to Jefferson even though he had been deeply involved in the plot from the very start.
The number of times Wilkinson was almost brought down, and managed to right his ship by ruining the credibility of his accusers and telling well-crafted, outright lies about the nature of his relationship with the Spanish authorities, is astounding. That he was finally brought down at all ends up being something of a surprise: even after a disastrous loss of troops to illness during the early days of War of 1812 Wilkinson was granted command of the operations to take Canada; when this effort failed spectacularly he survived yet another court-martial (Linklater writes that contemporary jibes had it that Wilkinson "never won a battle, but never lost an inquiry") and was only cashiered during the wholesale downsizing of the military at the end of the war. Even this embittered Wilkinson, who fired off angry letters in every direction and published a three-volume memoir in defense of himself. He ended his days in semi-exile in Mexico, dying there in 1825.
Some of the most breathtaking elements of Wilkinson's treason include his simultaneous memoranda to Jefferson and to his Spanish handlers instructing them (in practically opposite terms) how to deal with the American takeover of the Louisiana Purchase territory. Knowing of the Lewis and Clark expedition, for example, Wilkinson suggested to the Spanish that they might want to intercept the explorers (an attempt was made, but the effort failed). And Wilkinson's careful (and occasionally hysterical) efforts to protect his treason were of great interest: his payments were sent upriver hidden in barrels of foodstuffs, and he and his handlers used ciphers and codes to communicate with each other (an appendix documents some of the codes).
Linklater's book contains a few more than usual errors of the typographic variety, and he missteps (p. 188) in calling Burr the Federalist candidate for president in 1800 (John Adams was running for reelection, of course; Burr was ostensibly the Republican candidate for vice-president, but ended up being Jefferson's strongest competitor when the electoral college vote resulted in a tie and threw the election to the House). These aside, this is a good survey of Wilkinson's life and treasons. Vile he may have been (this is by no means a hagiography), Wilkinson's abilities to dissimulate and keep himself in the good graces of those who mattered were prodigious.