Final answer:
Interest groups support political parties based on shared ideologies, with pro-life groups typically backing Republicans and pro-choice groups supporting Democrats. Generational shifts influence party allegiance, with younger generations leaning towards Democrats and older ones towards Republicans.
Step-by-step explanation:
Interest groups align themselves with political parties based primarily on shared ideologies and goals. Political action committees (PACs) often contribute to parties that align with their interests, and by comparing party platforms to PAC contributions, one can see why certain groups support specific parties.
Pro-life organizations typically support Republicans because of the party's emphasis on conservative values, particularly opposition to abortion. Conversely, pro-choice organizations often support Democrats, who generally advocate for reproductive rights.
Party allegiance can also shift due to generational changes. For example, Millennials and Generation Xers show more support for the Democratic Party, likely due to liberal stances on various social issues, while the Silent Generation tends to support the Republican Party, which aligns with their more conservative values.