Candidates routinely shorten their campaign promises to match public opinion and to be very memorable. Common sense must be used in evaluating them though. Congress would have to pass the law to repeal Obamacare. So, every member of Congress that voted to do so would be held accountable for doing so. If elected, the candidate would be held accountable too.
While I agree that Obamacare is not perfect, it is definitely a decent start. One of Trump's main points has been that he is going to repeal Obamacare. Since he prides himself on being such an excellent businessman, I have yet to hear his actual plan of how he is going to fix it. So yes, a plan needs to be in place before the repeal cries should be heard.
Yes, it's very wrong for a politician to insist that Obamacare is repealed when he or she has no other solutions. Obamacare has helped thousands of people who previously were denied access to even basic healthcare. Obamacare gives everyone the opportunity to have health insurance. A person in our country can't get healthcare without health insurance. To get rid of this protection without providing another solution is wrong.
In order to take anything away that is a running program, there must be a plan to replace that program. This works with healthcare as well as anything else. Luckily Trump has provided a plan with what he believes will be a more effective way to deal with health insurance coverage.