Millionaire investors say the biggest risk to their personal wealth next year is dysfunction in Washington.

According to CNBC's latest Millionaire Survey, conducted by Spectrem Group, millionaires say they generally are bullish about the economy, markets and their own fortunes next year. But they also contend that political dysfunction and government debt are looming problems for the economy and their wealth.

The semiannual CNBC Millionaire Survey is representative of the affluent population in the United States. The survey analyzes the investment attitudes and behaviors of 750 investors with $1 million or more of investable assets. Respondents are required to be the financial decision-maker or share jointly in financial decision-making within the household.

The survey also highlights the fact that millionaire attitudes toward the economy and markets remain highly political, with 41 percent of Republican millionaires predicting the economy will be better in 2019, compared with only 8 percent of Democratic millionaires.

Fully 40 percent of millionaires surveyed say the economy will be just as strong in 2019 as it was in 2018, and 28 percent say it will be even better. Yet government dysfunction remains the greatest concern for investors regarding the economy (38 percent) and also to their own personal wealth (37 percent). Thirty-two percent believe the stock market has increased as a threat compared to the past, and worries over the national debt and immigration have increased.

While more than half of millionaire investors anticipate that the S&P 500 will be up more than 5 percent in 2019, 20 percent believe it will be flat.

When asked about their own returns, 37 percent said they expect returns of 4 percent to 5.9 percent, while 30 percent expect returns of more than 6 percent. Only 4 percent of respondents expect to be down in 2019.

Their longer-term outlook for future generations are also cautious: Only a third of millionaires say their kids will be better off than they are, while 37 percent said they will be worse off.