A country can tolerate growing debt if GDP is growing faster than debt because its growing income can pay its growing debt. The obvious warning sign is when debt grows faster than GDP. Negative consequences of this are (1) a country might not be able to repay debt; (2) cash must be added to the system to pay for these debts which increases inflation or deflates the currency or both; (3) taxes must be levied to pay for debt, which is difficult on an economy and can slow growth.
