The phrase "asserted once that" is correct and usable in written English.
It can be used when referring to a statement or claim made by someone at a specific point in time.
Example: "The researcher asserted once that the findings would change the way we understand climate change."
Alternatives: "claimed at one point that" or "stated previously that".
In response, he asserted once again that there had not been disagreements about the surveillance program, insisting that the dispute involved "other intelligence activities".
At 6 35 A.M. on Monday, a few hours before the House Intelligence Committee convened its first public hearing on Russian involvement in the U.S. election, President Donald J. Trump asserted once more that the issue was nothing more than an elaborate political distraction.
And we have to assert once again that government is not some far off entity that orders us around and intrudes into our lives.
It's telling that what the Brussels blog calls a "particularly nasty attack" was in fact a summary of Paul DeGrauwe's work indicating that European austerity has been deeply wrong-headed, in the course of which I quoted Mr. Rehn asserting, once again, that old-time austerian faith.
"We assert once again that Stephen Ambrose is one of America's most original and brilliant historians," Simon & Shuster spokeswoman Victoria Meyer said today.
Albert aimed to discover Aristotle's own meaning, with the help of Greek and Arab commentators who led him into disagreement with other Latini, including at certain points his pupil Thomas, and he asserts more than once that philosophy and theology are separate spheres of knowledge.
Before the invasion he had confidently asserted that once coalition troops showed up in Baghdad, rejoicing Iraqis would promptly lead them straight to the smoking-gun evidence he knew was there.
When Steve Kroft asserted that, once again, we are the ones leading the operation in the Middle East, Obama cut him off.
Dmowski asserted that once a Jewish state was established in Palestine, this would serve as a nucleus for the Jewish take-over of the world.
Moyle asserts that once potential tourists get past that negative image "they will find really nice and beautiful people, with a rich culture, living on this untouched tropical gem of North Queensland".
