It would have been tough - the only way really would be if the Soviets were still visibly making progress. If there had been some successful N-1 flights, or if the Zond program had beaten the US to a manned lunar flyby in late 1968 (which was very possible).
You can draw an analogy with companies - where competition means harder work, but ultimately benefits the consumer
How do you think US leaders could have convincingly justified space spending after they'd beaten the Soviets to the Moon?
It would have been tough - the only way really would be if the Soviets were still visibly making progress. If there had been some successful N-1 flights, or if the Zond program had beaten the US to a manned lunar flyby in late 1968 (which was very possible).
Political bragging rights or fabulous profits: those seem to be the two motivators!