I think the democrats have had their fair share cowboy The...

I think the democrats have had their fair share cowboy

The following Presidents are (or were) Democrats except as noted.

Widrow Wilson - President when the US entered WWI

Franklin Deleno Roosevelt - President when the US entered WWII

Harry S. Truman - President when the US entered the Korean War.

Vietnam is a bit tricky to name the President who was in office when the "war started".
Harry S. Truman actively supported the French in their Indochina War
Dwight Eisenhower (Republican) was President when the US agreed to supply up to 10,000 advisors to support the new South Vietnam state following the Paris Peace Talks in 1954.
John F Kennedy was President when the US expanded it's role in Vietnam to exceed the 10,000 advisory limit, started flying South Vietnamese troops to and from battle in helicopters, and started flying limited air strikes in South Vietnam.
Lyndon Johnson was President when the US involvement escalated to the point where we had a half a million troops in Vietnam and was conducting and ongoing air war against North Vietnam.

President Clinton was in office when the US was involved in a the NATO air campaign in Kosovo.

During President Obama's Administration, the US was actively involved in pre-existing wars in Iraq and Afghanistan but also engaged in a air campaign to oust Gadaffi in Libya and reengaged in Iraq and now Syria to fight ISIS.

Note that the only Democratic President since the start of the 20th century NOT on the above list is Jimmy Carter.