Back in 1808 New York City was a small town located at the south end of Manhattan Island -- the rest of the island was merely farm and pasture land. But the ambitious New York City Mayor De Witt Clinton had great plans. He created a map where he laid out where the future streets would go. Clinton hoped that New York would expand northwards in time to fill up the entire island. Sure enough, by 1850, New York had grown and had become the largest city in the world. The old America was a place filled with "big dreamers" and their 'big dreams" who thought that anything was possible. Even as late as 1963, President John F. Kennedy pledged that the United States would land a man on the Moon by 1970 -- even though at that moment Kennedy had no idea how to accomplish this incredible feat. But by 1969, the American flag had been planted on the Moon. Today, as we seem unable to solve our many problems (and acquire new problems every day). It looks as though America is no longer filled with confident "big dreamers." Do you agree or disagree with this negative assessment of the United States in 2018?

When answering this question I think you would be best off seeing if you can find examples of Americans overcoming great problems of the current day. I understand that it can all seem like doom and gloom if you are just watching the news highlights, but I would challenge you to see if there really is nothing akin to the growth of New York City or the space race happening today being accomplished by the "big dreamers" of the country.
I'll give you a few examples you might want to consider. Elon Musk is certainly a big dreamer. He seeks to completely transform the way people travel both on Earth and off the planet. While he is not without his own controversies, you should consider his goals to be as audacious as De Witt Clinton or President Kennedy.
You might also consider Sheryll Sandburg, the chief operations officer at Facebook. She is simultaneously growing the world's largest social network and striving to create an even playing field for women in the workplace.
These are just two people you might consider to start off with. I would argue that there are still many American visionaries out there. The difficult part of identifying the big dreamers of today is that their dreams are still uncompleted, and therefore we do not have the historical perspective by which we can analyze and consider their accomplishments.
One final note to consider: America has always had its issues that it has struggled to overcome. In Mayor Clinton's time, there was legalized slavery and oppression of just about every minority in the country as well as a major financial crisis. Kennedy's time had its issues as well. All this is to say that no time in history was without both its setbacks and its visionaries.