Christian Nationalism and lusting after political power
We should always distrust out own hearts and motivations, because we are corrupted by sin.
King David wrote in Psalm 20:7 that it is better to trust in God than chariots and horses. David was a humble man, telling the people under his authority to trust God rather than him and the army under his command.
I think much of the criticism of Christian nationalism is overwrought. What is condemned today as "Christian nationalism" is not much different from plain old Christian conservatism of the 1980's and 1990's. It's been given a different name to convince people this is something new. On the Left, that is done to scare people. On the Right, this is done to give people hope that a "new" political movement will restore our nation.
One of the things that is not different, and that Christians should be on guard against both in ourselves and in our leaders, is lusting after political power for its own sake. Putting a Christian label on a desire for political power for its own sake does not make it any less spiritually dangerous. We must always be careful to place our trust in God, not in a political leader or political party who says he will either lead us into the promised land or protect us from the "bad guys."
This is a constant tension for Christians involved in public policy - whether advocating for sound policy as a private citizen or implementing it as an elected official. It is good for Christians to be involved in the public square, including running for political office, serving in a non-elected capacity in government, or seeking to influence political leaders. We should hope to see God's Moral Law reflected in our laws, for the protection of the innocent and to restrain the worst impulses of the wicked.
But we should not seek power for its own sake. Christians should not enter the political arena in order to seek personal power, influence, wealth or fame. Advocating Christian morality in public policy should always be done with the intention of serving God. This is a constant tension and a constant temptation for Christians in the public sphere: When are we crossing over to serving ourselves and not serving God? We should listen to wise counsel and ask God to reveal to us our own hearts, always praying to Him for guidance, wisdom and discernment.