Winnable vs Unwinnable Wars

Why is it, that whenever the Dems or Progressives or Leftists or Peaceniks or whatever decade we are in, talk about war, they always raise the question, "is this a winnable war?" Every war America becomes involved in, including the ones in Iraq and Afghanistan, are winnable!
This concept has only come into vogue since the late 1960s. Korea was fought to a truce because the Chinese got involved and we decided to enter into the truce because we did not want to use atomic/nuclear weapons.
In the late '60s (Vietnam War), we had LBJ and his "Guns and Butter" (Google that phrase) concept. The Progressives wanted to transfer wealth and abandon the war against Communist expansion, so it became "unwinnable". But we eventually beat the Communists under Reagan, much to the chagrin of the Dems/Progs.
The First Gulf War was too short for the Dems/Progs to raise the issue of winnable/unwinnable.
Now that we have a Dem/Prog admin and legislature (even though the wars were going well under a Repub admin and Legislature in spite of the Dem/Prog opposition), the issue of a winnable/unwinnable war is once against being discussed.
We beat the Germans and Japanese and rebuilt Europe and Japan. I cannot be convinced that we cannot win whatever war we face.
We lose 35,000 people (mostly young and promising) to DUI accidents every year and we say and do very little about it. In contrast, we lose about 800 brave young men and women each year to hostilities and the anti-war crowd goes berserk. I am glad that they pay lip service to our heroes' sacrifice. I am not belittling the sacrifice of these young men and women nor of their families. I have been there: an Infantry Platoon Leader and Company Commander in Vietnam late June '67 to late June '68. I became a Commander during Tet-'68. I am just saying that we have the tendency to lose perspective. At least our heroes' deaths are for a purpose, a cause - freedom and offering the ability to choose to millions. These heroes decided that freedom and choice was worth the risk. One death offered to protect their loved ones' freedom, which flows from patriotism vs. four hundred deaths, inflicted by really bad judgment. We need to get a grip, get involved loving our veterans and our heroes' families and get the job done.