Like Reuben Fine, Kashdan, one of the strongest US players ever, never won the US Championship. In 1942 he came close.
After a lot of controversy the whole tournament hinged on a single move, but it was not a move by Kashdan. It was a move by 6th place finisher, I.A. Horowitz.
The most controversial US championship ever was the one held in 1942. It began on April 10, 1942, five months after Pearl Harbor and there was doubt that there would be a U.S. championship for several years. The USCF had sent out an announcement in January cancelling the championship because "The United States Government has issued a call for an all-out struggle in a war which has been thrust upon us," adding, "Our way of life is in great peril ... [and] the present time is not propitious for holding a championship tournament.” In his Chess Review magazine Al Horowitz was against the cancellation, pointing out that Washington had encouraged the continuation of professional sports and that other nations at war - such as Great Britain - had continued the traditions of chess despite the fighting. The USCF relented and the top players agreed to forego appearance fees and guarantees of prize money agreeing to play for modest prizes.
The result was that the tournament was not a very strong one, several of the stronger players being unavailable for various reasons. Actually, out of the 16 players there were only seven real contenders: Reshevsky, Kashdan, Denker, Steiner, Pinkus, Horowitz and Seidman.
One of the biggest disappointments of Kashdan's career was his failure to win the US Championship and the 1942 tournament was probably the bitterest of all. This tournament was a race between Kashdan (+11 -1 =3) and Reshevky (+10 -0 =5). Kashdan would have been U.S. champion in 1942, but for two unfortunate incidents over which he had no control.
The first happened in the 6th round when the tournament director, the infamous L. Walter Stephens, incorrectly forfeited Denker after Reshevsky exceeded the time limit. Reshevsky had been winning but one move before the time control he threw it away. Denker, also in time trouble, played the drawing move and when he punched the clock, Reshevsky's flag fell. Stephens, standing behind the clock, picked it up and turned it around so that the clocks were facing opposite sides and then declared Denker forfeited. Despite howls of protest from Denker and the spectators, Stephens refused to change his decision. When asked, Reshevsky replied, “It’s not my decision.”
Reshevsky opened up a lead over Kashdan when Kashdan overlooked a brilliant queen sacrifice by Hreman Steiner and lost. But in the next round Reshevsky could only draw against the last place finisher, a minor master from Chicago by the name of Herman Halhbohm.
After his last round game finished Kashdan had a 12.5 – 2.5 score and he sat down to watch the Reshevsky-Horowitz game. Reshevsky was at 12 points and so the result of that game was critical. Horowitz outplayed Reshevsky and adjourned two pawns up.
After Denker's 45th move Kashdan observed that to the spectators it looked to be all over, but opposite colored bishops and Reshevsky's better placed king offered drawing chances. Kashdan later wrote, “I refuse congratulations, wondering what it will be like to be champion .... It has been three long weeks. I am thinking back to 1934 when I challenged Frank Marshall to a match for the American championship and the number of times I have tried for the title since. This is my best. Just a few good moves, friend Horowitz .... "
Indeed, Horowitz made good use of his extra material for the next several moves. But then came Horowitz' 58th move. It allowed Reshevsky to draw and Reshevsky had another last-round miracle that resulted in co-champions for the first time in the history of the US Championship.
The result was a playoff. The playoff was a 14-game match which began in October and was held at US Army camps for the benefit of the troops. The match seesawed back and forth for the first four games but when the match returned to New York City for the fifth game Reshevsky took the lead and never relinquished it, finishing +6 -2 =3. Here's the Reshevsky vs. Horowitz game.