It used to be almost impossible for another team to get a manager out of his contract. While it has happen before, there has been a sort of etiquette which has kept teams from prying away other team's managers. The only time a manager ends up going to another team or gets traded is when it is the manager's choice to do so. In other words, the manager is the one who wants to go to the other team and only then does his employer decide to seek compensation. In fact, in the case of Art Howe wanting to manager the Mets, the Athletics simply just let Howe out of his contract.
Some examples of managers getting out of their contracts to switch teams are John Farrell, Lou Piniella and Ozzie Guillen. Piniella and Guillen were returning home and Farrell always wanted the chance to manage in Boston. Compensation was sent in each prior case.
Porter, 41, played in the big leagues for the Cubs, Athletics and Rangers from 1999-2001. After his playing career ended, he managed two seasons in the Florida Marlins minor league system (2005-2006) before getting a job on the coaching staff for the 2007 season. He remained there through 2009 and took a job as 3rd base coach for the Arizona Diamondbacks for the 2010 season. When Kirk Gibson became manager mid season, Porter became bench coach. After he was let go after the season, He joined the Washington National coaching staff and was the 3rd base coach in 2011 and 2012. The Astros hired him after 2012 to be their manager, but Porter was also a finalist for the Florida Marlins and Pittsburgh Pirates managerial vacancies after the 2010 season.
It obviously has the most to do with what Porter wants to do. I doubt it would be a decision about the talent level of the Astros and Nationals, but it could be. I am sure Porter was 100% on board with the Astros rebuilding process and would like to see it through. But what if he had Washington on his mind? What if he had been given the thought he had a chance to succeed Johnson? I would assume he would have turned down the Houston job since odds were Davey Johnson would manage his last season in 2013. This is why I think Porter will stay in Houston. In my opinion, the Porter ties to Washington are not as serious as the Farrell/ Boston ones. All the time Porter took to familiarize himself with the Astros organization would be enough for him to stay. There is also a report that, while Porter did not necessarily have any say in the players the Astros most recently drafted, he may have been confided in a little bit. Both Porter and the Astros are probably set for Bo to be around for the next several seasons. But then again, would it surprise anybody if Nationals GM Mike Rizzo made an inquiry?