I remember a teacher in my American history class referred to a president that brought the Republican Party out of popularity, allowing the democrats to pull ahead in many of the elections. If this is true, who caused this and how?
It's hard to know on such scant information provided, but two possible candidates:
Theodore Roosevelt, formerly a Republican President, tried to regain the Presidency by running as a third-party candidate. This opened to door to Woodrow Wilson being elected as the first Democratic President in 20 years.
Herbert Hoover was president during the stock market crash of 1929. His minimalist approach to responding to the crisis was so unpopular that no other Republican was elected President until 1952.
Would you know the time period involved? This could describe any number of periods since the founding of the two parties.