Yes, one spouse can be held responsible for mortgage debt incurred by the other spouse during a trial separation, depending on the specific circumstances and the laws of your jurisdiction. Here are some factors to consider:

1. Community property: If you live in a community property state, both spouses may be responsible for debts incurred during the marriage, including during a trial separation.

2. Joint ownership: If both spouses own the property together, they may both be liable for the mortgage debt, regardless of who incurred it.

3. Co-signing: If one spouse co-signed the mortgage or loan documents, they may be legally responsible for the debt.

4. Court orders: A court may order one spouse to pay the mortgage debt as part of a temporary or permanent support order during the trial separation.

5. Separation agreements: If the spouses have a written separation agreement, it may address who is responsible for the mortgage debt.

To determine responsibility for mortgage debt incurred during a trial separation, consult with an attorney specializing in family law to understand your specific rights and obligations.