Do Presidents Change After Taking Office?

I mean, im sure they change, but i just realized something..when a president gets elected, ESPECIALLY now days its more of a popularity contest. People really dont know their politics. Including myself. I used to keep up in highschool but after a while politics became extremely stressful to stress over. lol i just remember being pissed about how some politicians who are completely ignorant, call the shots. 
 
Quick example..Americas the land of the free. Governed by the people..A majority of us want weed legalized, but have a national vote on it would NEVER happen. Its all about laws and acts getting approved by POLITICIANS..
 
my god i get fucking distracted..
 
Anyways, when a president gets elected, that first day on the job.. they have NO IDEA what there in for. and im sure they realize after a while that all their optimism and promises during there campaign was a little unrealistic.Theres too many things to do. And once you turn your focus on one issue, the media can make it seem like the president avoiding the issues that 'matter' Besides, the only issues that matter are the ones the mainstream media talks about. Really, the mainstream media has a huge influence on what people would consider "current issues". 
 
I know im not doing a good job at explaining this but i do notice that Obama seems worn out. Like he wakes up some days and just has to put on a face for the cameras. theres no turning back right? you're elected.It also seems like a majority of people disapprove of the job he's doing.
 
But do you think theres a process that presidents go to, that only other presidents can understand. like they think to themselves "i cant believe i thought i was gonna get all this shit done".. i remember in 2008 when i was in the 8th grade seeing obama as a NEW kind of president. He made the CHANGE thing seem like a legit promise. Its not that he lied. He just has no idea what hes getting into..Hes just like the other presidents.