The Marshals had a warrant for Weaver as issued by the judge for not showing up to his hearing (because his summons had the wrong date on it).
That is not correct. Weaver was originally given a trial date of February 19. The court changed that to February 20th, and attempted to notify Weaver, including trying to notify Weaver through his lawyer.
The wrong date was on a letter sent by the officer working for US Probation that was supervising Weaver while released on bond. The letter references the trial date, incorrectly, but was a letter asking why Weaver was not complying with the conditions of bond set by the court. You see Weaver was already in violation of the conditions of bond when that letter was sent. Weaver had already started to act in a manner hostile to the court. Regardless, the correct date had been sent to Weaver and his lawyer by the court clerk. However, Weaver was already refusing to communicate with his attorney.
So Weaver was violating the conditions of bond, refusing to communicate with his attorney, and then Weaver did not show up for court, either on the correct date that the court and his attorney tried to notify him of, or the incorrect correct date referenced in a letter about his failure to comply with conditions of bond.
Despite the fact the court and his lawyer actually did attempt to notify Weaver of the correct court date, IMO you'd have a decent point if the USMS had tried to arrest Weaver before the incorrect March 20 court date referenced in the letter from the probation officer. However, they did not do that. In fact they didn't arrest him immediately following March 20th. Instead they attempted to get him to come to court for a year and a half. In that time the Randy and Vicki Weaver made threatening statements, and the ENTIRE family (including Sam Weaver) was known through surveillance to be prepared for an armed confrontation with law enforcement.
The DUSMs that were on the Weaver property in August of 92 were attempting to recon the property in preparation for an operation that would hopefully allow the USMS to arrest Weaver without violence. Unfortunately Randy Weaver, Kevin Harris, Sam Weaver and the family dog went out and confronted them and a shootout resulted.
However, let's not pretend that one typo from the probation officer gave Weaver justification for his actions, especially considering the court clerk and his lawyer tried to get him the correct court date, and no attempt to arrest Weaver was made before the incorrect later date referenced in the probation letter. Further, Weaver had already been violating the conditions of his bond prior to the probation officer sending out that letter.