What is the exception that allows an officer to make a warrantless arrest for a misdemeanor?

The correct answer is based on the principle that officers are permitted to make warrantless arrests for misdemeanors when they have probable cause to believe that the individual is committing, or has just committed, an offense. In particular, driving under the influence (DUI) is a serious offense that can lead to significant risks to public safety. Therefore, if an officer observes behaviors consistent with DUI, or if they have credible information pointing to such conduct, they are justified in arresting the individual without a warrant. This allows law enforcement to act swiftly to prevent potential harm.

In contrast, warrantless arrests based solely on consent, evidence of a prior offense, or merely based on a crime being reported may not necessarily meet the legal threshold set forth for immediate action in the case of a misdemeanor. Consent does not always justify the lack of a warrant if the situation does not involve an ongoing or imminent crime. Similarly, having evidence of a prior offense does not provide a basis for arresting someone for a current misdemeanor without witnessing or having robust probable cause. Finally, a mere report of a crime does not automatically confer authority to arrest without additional evidence that supports the officer's justification for doing so at that moment.