Former U.S. President George W. Bush expressed his concerns that the 9/11 terror attacks could become a distant memory, while promoting his memoir?in Chicago?on Thursday, according to Chicago Tribune.

Smoke and dust engulf much of lower Manhattan and the area around the World Trade Center in New York, in this September 11, 2001 handout file photo taken by the New York City Police Department and obtained by ABC News, which claims to have obtained it under the Freedom of Information Act. [Xinhua]

Bush worried that the September 11th," a scar of heart" will become a distant memory, just like the Pearl Harbor day. And he also reminded Chicagoans that they should not forget that the Sear Tower in Chicago, now known as the Willis Tower was also on the list of possible targets for the 9/11 hijackers.

Bush praised Chicago Mayor Richard Daley, who has joined him at the Union League Club downtown Chicago, along with all Chicagoans for their brilliant response on the day of the attack, including enhancing security at the tower and evacuating downtown.

Bush attributed Chicago as the "best-run city in America" due to Daley's leadership. And Daley spoke highly of Bush for his calmness in the face of pressure on the day by saying "he stood very calm with leadership qualities and bringing people together on behalf of a great nation," according to Chicago Sun-Times.

The ex-president, who had kept a low profile since leaving office, has been on a book tour to promote his book, "Decision Points," which hit store shelves Tuesday. Bush defended his legacy and decisions by going through various flash points of his presidency in his memoir.

Bush summarized in the book that his most meaningful accomplishments as president was "America went seven and a half years without another successful terrorist attack on our soil."