The Republican Party holds a press conference announcing their stance on a new law. The Libertarian presidential candidate presents his political platform before Congress. The Democratic Party calls millions of citizens to remind them to vote for the Democratic candidate. Members of the Republican Party join and donate to a political action committee. Which is an example of how a national political party influences a political campaign?

The correct answer is "The Democratic Party calls millions of citizens to remind them to vote for the Democratic candidate."

This is an example of how a national political party influences a political campaign because the party uses every tool and power it has at hand to mobilize all their followers to support the campaign efforts on the streets, in social media, TV & Press ads, and media interviews, in order to guarantee the best chances of victory in the election.

The best example contained here is: The Democratic Party calls millions of citizens to remind them to vote for the Democratic candidate

In this example the Party is using their collective power to mobilize and to get people out to vote for a particular candidate by directly appealing to the people.