The phrase "asserted again" is correct and usable in written English.
It can be used when indicating that something has been stated or claimed once more after a previous assertion.
Example: "The scientist asserted again that climate change is a pressing issue that requires immediate action."
Alternatives: "reiterated" or "restated".
We must be ourselves, he asserted again.
Mr. Lazio asserted again yesterday that he had done nothing wrong.
But they often do not work perfectly, Mr. Morris asserted, again citing the fund's own data.
Senate Majority Leader Mitch McConnell immediately asserted again that nobody would be confirmed before the 2016 elections.
Mr. Schrempp asserted again today that his strategy was correct, and that the problems were merely operational in nature.
The lawyer asserted again that the boy was happy to be with his father, stepmother and infant half-brother.
It starts by asserting again and again that reducing the deficit is a progressive endeavour – we seek to balance the books because it is the right thing to do.
Bloom works the other way, reading forwards from the absolute primacy of Shakespeare, and asserting again and again that we cannot escape from him, that he assimilates us, not the other way around, that he reads us.
Doing so shifts the conversation from one in which you assert (again) what you want to one in which you're required to honestly examine why the other person might want something else.
The fourth major Democratic candidate, Peter F. Vallone, presented himself as the staid and mature government official, asserting again that Democrats should choose him to succeed Mayor Rudolph W. Giuliani because Mr. Vallone had played a central role, as the City Council speaker, in pushing through programs that had improved New York's fortunes over the past 10 years.
Fragment 17 provides us with the only further evidence for Philolaus' cosmogony, asserting again that the cosmos began to come to be at the middle and adding that it developed symmetrically around the middle.
